A public blockchain is a blockchain that anyone can join and participate in, such as Bitcoin. Disadvantages may include: the vast majority of public chain systems require high hardware resources for security, and there is barely no privacy for transactions on the public blockchain. While, these are what blockchain companies concern greatly for use cases.
A private blockchain network is similar to a public blockchain network in that it is a decentralised peer-to-peer network. The significant difference is the entire network of private blockchains is managed by a single organization. This organization has full authority to control who is allowed to participate in, and maintain the blockchain network. Depending on usage situation, trust and confidence among participants can be significantly increased. Private blockchains can run behind corporate firewalls and can even only be managed within the organization.
Multiple organizations can share the responsibility of maintaining the blockchain. These pre-selected organizations will decide who can submit transactions or access data. Consortium blockchains are ideal for business where all participants need to be licensed and have joint responsibility for the blockchain.