Write permissions are kept centralized to one organization. Read permissions may be public or restricted to an arbitrary extent. Example applications include database management, auditing, etc. which are internal to a single company, and so public readability may in many cases not be necessary at all. In other cases public audit ability is desired. Private blockchains are a way of taking advantage of blockchain technology by setting up groups and participants who can verify transactions internally. This puts you at the risk of security breaches just like in a centralized system, as opposed to public blockchain secured by game theoretic incentive mechanisms. However, private blockchains have their use case, especially when it comes to scalability and state compliance of data privacy rules and other regulatory issues. They have certain security advantages, and other security disadvantages (as stated before).

In October 2014, the MIT Bitcoin Club, with funding from MIT alumni, provided undergraduate students at the Massachusetts Institute of Technology access to $100 of bitcoin. The adoption rates, as studied by Catalini and Tucker (2016), revealed that when people who typically adopt technologies early are given delayed access, they tend to reject the technology.[85]
These kinds of blockchains are forks of the original implementations but deployed in a permissioned manner. Mainly hyped because the companies behind these chains want to onboard corporations in order to generate buzz around their their chain. It’s tolerable for proof of concepts or if they plan to move to public as soon as possible; otherwise they are just using the wrong set of tools for the job.
@gendal I am discussing private chains with prospects, so my interest is not superficial and theoretical. I see the benefits for the organization in using the private chain as another form of internal database, with better security properties. It can also be used where a service bus product would be today, to facilitate integration, conformance, monitoring, audit. Private chain can also, via a two way peg, be connected to the main chain, achieving a form of public/private network divide that routers created for us in the early stages of the Internet development. Anything else on the benefits side that I missed?
Another technology that could see more widespread use in the coming years is side chains. A side chain is defined for one specific use case. There can be multiple side chains where different tasks are distributed accordingly for improving the efficiency of processing. Maybe one application needs to optimize for high speeds and another needs to optimize for large computations. In any case, side chains can be used to handle commercial blockchain usage. CryptoKitties would have greatly benefitted from an optimized high-speed side chain. At one point, they jammed up the Ethereum blockchain with 25% of all transactions coming from their application.
“Further, contribution is weighted by computational power rather than one threshold signature contribution per party, which allows anonymous membership without risk of a Sybil attack (when one party joins many times and has disproportionate input into the signature). For this reason, the DMMS has also been described as a solution to the Byzantine Generals Problem[AJK05].”
Sidechains, just like any other Blockchain, need their own miners to help protect them from nefarious actors and attacks which people would like to leverage against the network. However, since wealth isn't actually created on the Sidechain there is far less incentive for miners to actually work on it and help protect it. Because of this, transaction fees are the basic reward that is offered to miners. However, these often equate to mere pennies.
Decentralization and distribution are seen by many to be a major benefit of public blockchains, but not everybody shares this ethos. But this is not the only benefit of public blockchains, of course. Perhaps most importantly, their transparency makes them very secure: because they can be audited by anybody, it is easy to detect fraud on the chain. Security-via-openness is a principle well known in the open source world, and this strategy is also popular among some in the digital currency community. For example, all of the tools and content produced by the Ethereum team is open source. This helps to make Ethereum widely accessible and more secure.
Cohen said Walmart also has a patent on drone delivery systems that facilitate orders in a cleaner way, track package contents, environmental conditions and location. Walmart supplier Coca-Cola is starting a pilot to use blockchain to identify inhumane labor conditions in its sugar supply chains. Coca-Cola plans to create a secure decentralized registry for workers and their contracts to help securely record their workers’ identities while providing a trail in case employers abuse their power.
Jump up ^ Redrup, Yolanda (29 June 2016). "ANZ backs private blockchain, but won't go public". Australia Financial Review. Archived from the original on 3 July 2016. Retrieved 7 July 2016. Blockchain networks can be either public or private. Public blockchains have many users and there are no controls over who can read, upload or delete the data and there are an unknown number of pseudonymous participants. In comparison, private blockchains also have multiple data sets, but there are controls in place over who can edit data and there are a known number of participants.
Plasma, a project by Ethereum, uses this side chain concept. It encourages transactions to happen on side chains (or child chains). An authority governs each of the child chains. If the authority starts acting maliciously, anyone on the child chain can quit the child chain and take back their pegged assets on the main chain. It’s in its early stages of development but shows a lot of promise in handling some of Ethereum’s scalability issues.
Public chains to the rescue! Public chains offer public transaction data that can be verified in real-time by anybody that cares to run a node. The more independent users or institutions that take part in verification, the more secure and decentralised the chain becomes! At Iryo, we strive to have every clinic doing full validation of the global state for the relevant smart contracts (EOS based). Public blockchains are mainly useful for two things; value routing (including initial creation and distribution) and trustless timestamping of messages.
“Further, contribution is weighted by computational power rather than one threshold signature contribution per party, which allows anonymous membership without risk of a Sybil attack (when one party joins many times and has disproportionate input into the signature). For this reason, the DMMS has also been described as a solution to the Byzantine Generals Problem[AJK05].”

Alpha functions as a sidechain to Bitcoins testnet. The peg mechanism currently works through a centralized protocol adapter, as stated in the sidechains whitepaper. An auditable federation of signers manages Testnet coins transferred to the sidechain. The federation is also relied upon to produce blocks through the signed blocks element. This creates the possibility of exploring the possibilities of the new chain using different security trade-offs.
The “three-part” transaction structure is very general but it only allows you to transfer ownership of Bitcoins. Some people would like to transmit richer forms of information across these sorts of systems. For example, a decentralized exchange needs a way for participants to place orders. Projects such as Mastercoin, Counterparty, NXT and others either build layers on top of Bitcoin or use entirely different codebases to achieve their goals.

The immense promise and accelerated development of permissioned blockchain technology, combined with intense business interest from a wide range of industries, is acting as a perfect stimulant for more and more enterprises to start rolling out blockchain networks into production. I envision these permissioned networks will soon directly or indirectly influence every facet of human enterprise.