Private blockchains, or as I like to call them, shared databases, have a place in improving efficiency for financial institution for back-office settlement processes. They should not be seen as controversial, or part of some dialectic struggle between punks and police. To the extent that the identifying shroud of AML/KYC can be placed into public blockchain metadata (possible in Omni Layer transactions over the Bitcoin blockchain) there may even be interoperability between these two sides of the train tracks. Right now, due to state-granted monopolies to issue credit, most of the world's liquidity is still in banks. However, we believe that in the long-term, public blockchains, especially those based on work, will come to take a more significant part in the ‘System D’ informal economy, which is where most of the global economic growth will originate.” 

– A cost per transactions which can be high: Miners only participate in the process of mining because they hope to get the reward (coinbase and fees) allocated to minors who have added a block to the blockchain. For them it is a business, this reward will finance the costs they have incurred in the process of mining (electricity, computer equipment, internet connection). Tokens that are distributed to them are directly issued by the Protocol, but the fees are supported by the users. In the case of the bitcoin, for example, minors receive 12.5 bitcoins for each block added, to which are added fees paid by the users to add their transactions to the blocks. These fees are variable and the higher the demand to add transactions, the higher the fees.
Start preparing for STO in a week with a professional blockchain development team. We have real experience in the following platforms: Ethereum, Stellar, Hyperledger, EOS We developed the world’s first platform for real business assets tokenization on Stellar that raised 1,700,000$ ! SheerChain is a custom software development company and a trusted IT outsourcing provider for our clients worldwide. Combinin ... Read more
At Iryo, we consider databases and blockchains that are not opened to the public to be insecure they, can easily be altered by the business running it, at their discretion and it goes against the ethos of the open and transparent cryptocurrency space. Designed to keep public out and introducing “trusted” middlemen, private chains forget that trusted third parties are security holes.
Consider a proof-of-existence application, where you want to authenticate your document in the Ethereum (for example) network, but you do not need your document to be online. So, you will store the hash generated from your document in the blockchain, but the document itself will be in your local machine, out of any blockchain-related structured, being off-chain.
Structure	Side chains are independent blockchains that have a kind of "pegging mechanism", where at least one of the chains (main chain and side chain) is "aware" of the other chain and both tokens are pegged at a set ratio. Side chains need their own network security and block processing.	"Child Chains" of the Ardor platform are tightly integrated into the main Ardor parent chain. All transactions are processed and secured by the parent chain forgers. This makes cross-chain transactions possible. Pruning will be enabled on child chain transactions in order to significantly reduce blockchain bloat by pruning the transactions on regular basis from the blockchain.

Jump up ^ Shah, Rakesh (1 March 2018). "How Can The Banking Sector Leverage Blockchain Technology?". PostBox Communications. PostBox Communications Blog. Archived from the original on 17 March 2018. Banks preferably have a notable interest in utilizing Blockchain Technology because it is a great source to avoid fraudulent transactions. Blockchain is considered hassle free, because of the extra level of security it offers.
The second option will be to use sidechains. Blockstream first announced side chain in 2014 and published its whitepaper ( I believe in the future, bitcoin will have its desired flexibility with its sidechains. The idea of the sidechain is you can innovate and design your solution freely in the sidechains. These sidechains are independent, if they are failed or hacked, they won't damage other chains. So damage will be limited within that chain, for that reason you can be less conservative. Otherwise you would be more risk averse, if you had 42.5 billion dollar market cap like Bitcoin.
“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].”
In this case, you work directly with the given blockchain tools and stack. Assembly is required, so this isn’t for the faint of heart at this point, as many of the technologies are still developing and evolving. However, working directly with the blockchain provides a good degree of innovation, for example in building decentralized applications. This is where entrepreneurs are creating ambitious end-to-end, peer-to-peer applications, such as OpenBazaar (on Bitcoin), or Ujo Music (on Ethereum).
Blockchain-based smart contracts are proposed contracts that could be partially or fully executed or enforced without human interaction.[55] One of the main objectives of a smart contract is automated escrow. An IMF staff discussion reported that smart contracts based on blockchain technology might reduce moral hazards and optimize the use of contracts in general. But "no viable smart contract systems have yet emerged." Due to the lack of widespread use their legal status is unclear.[56]