Private blockchains are also called organizational or permissioned blockchains. Organizations require the levels of security, privacy, compliance, performance, and many other features that a private blockchain can provide.
Transactions are processed by selected nodes on the blockchain. From a performance perspective, here only a handful of nodes process transactions, while in the case of Ethereum, 12,000 nodes can actually improve performance in terms of transaction speed and response time.
Transactions are not publicly visible on the blockchain, and only selected nodes on these private blockchains can access the ledger.

Advantages of Private Blockchains
1- Organizational Permission
The organization controls the resources and access to the blockchain, so these blockchains are private or permissioned.
2. Faster transactions
When nodes are distributed locally and there are fewer nodes to contribute to the ledger, performance will be faster.
3. Better scalability
The ability to add nodes and accessible services can be a huge advantage for organizations.
4. Adaptive support
An organization will likely have adaptive requirements that it needs to adhere to. Controlling the infrastructure by the organization itself will enable this requirement to be met.
5. Consensus will be more efficient due to fewer nodes.
Private blockchains have fewer nodes and usually have a different consensus algorithm. For example, BFT versus POW.

Are public blockchains more secure?
Public blockchains are designed to eliminate intermediaries and the need for trust in the network by offering rewards to participants. It is true that the more decentralization, the more secure the blockchain. Perhaps the transparency of a public blockchain is what attracts a wider range of uses. With more nodes on the network, it will certainly be harder for hackers to attack or take control of the network through a 51% attack; but it also slows down the network. Public blockchains like Bitcoin are no match for the centralized payment processors on the market like Visa, which can process 24,000 transactions per second.
In order to process more transactions per second, restricting access to information with specific functions is exactly what private blockchains are trying to achieve. Private blockchains can process more transactions than public blockchains; but is the increased transaction speed worth sacrificing security? Private blockchains are also generally much more vulnerable to hacking and data manipulation.

It’s All About Trust
Public blockchains like Bitcoin and Ethereum are designed to protect the anonymity of transactions. This is why cryptocurrencies are built on public blockchains. At the same time, in the corporate blockchain space, we are seeing businesses adopt private blockchains because they are not willing to be completely transparent or share all their business information with competitors. Private blockchains ensure that they have complete control over who can write and read the details of the information on the chain.
When it comes to which blockchain is superior to the other, it should be said that public blockchains seem to have better features due to their ability to be used in most applications and situations and without restrictions on access. At the same time, privacy issues exist in both blockchains. Many people think that these blockchains are competitors to each other, but in reality, this is not the case. The two blockchains are simply trying to provide different solutions.
The key difference between public and private blockchains is the level of access permission granted to network participants. Public blockchains are permissionless and decentralized. All users can verify transactions and add their information to the chain. A public blockchain is completely free and has open-source computational code that can be reviewed and downloaded by those who want to become full nodes or miners. Private blockchains are more centralized because they only allow certain people to participate in a closed network. In a private blockchain, all validators know each other and are installed as part of the network, and have the ability to change or modify transactions based on their needs. As a result, a private blockchain is more susceptible to a 51% attack because it is easier for malicious nodes to gain control of the network. Another key difference between public and private blockchains is scalability. Scalability is a major issue in the cryptocurrency space, especially for older coins like Bitcoin, which can only process 7 transactions per second. Currently, Hyperledger can process up to 20,000 transactions per second, thus maintaining the speed and efficiency of its network for users. Public blockchains are usually slower because there are more valid participants. As a result, these blockchains process transactions with a delay; while in private blockchains, transactions do not need to pass through hundreds or thousands of nodes to confirm their information. Therefore, these transactions can be supported and processed much faster.
The concept of decentralization may be to provide transparency, security, and reduce costs, but ultimately it all depends on the goals of those adopting the technology.