A public chain doesn't have restrictions, anyone with an internet connection on computer or phone can get access to the network and start validation blocks and sending transactions. Usually, that type of networks tend to give some sort of incentive for users who validates the block.
The network incline to use Proof of Work (PoS) consensus algorithm for authenticating the transaction.
Open and transparent
All transaction data are openly available for verification. The transparency of a public chain is also the main feature that gives hope for a wide range of use cases, from voting to financial transactions. Also, anyone can check the authenticity of transactions and recorded data.Secure
The more decentralization and active participation which essential, will determine how secure the blockchain will be. In other words, the more nodes there are in the system, the harder it will be for hackers to penetrate the network. In a public network, anyone can engage in the maintenance of a node or be a full minor and partake in the security of the network. It will very difficult and almost impossible for hackers to come together and work together to take control of the consensus network.No need for trust
The goal is to remove intermediaries in any form and more essentially, to remove the need for trust that business actors must impose in them for the easy running of the operations.
Adaptation
Public Chains can't compete with traditional systems that can handle large quantities of transactions. The more users grow, the more transactions to process in the system increase and the slower the public chain will be.Energy consumption
For instance, bitcoin's consensus algorithm Proof of Work, uses a certain amount of electrical resources to run, which has raised environmental concerns. Public chain like bitchain consumed much electricity or even much as 5% of the world's energy consumption used to produce Aluminum. Energy consumption will be one of the main disadvantages. It is also to see to address this problem than a lot of other consensus mechanisms have emerged, much less energy consuming, like Proof of Stake (PoS), and the Delegated Proof of Stake (DPoS)Slow
It is not surprising that public Blockchains are slow. For instance, bitcoin can process 7 transactions per second while ethereum can process 15 transactions per second. Ont the other hand, a centralized payment processor such as visa can execute more the 30,000 payments. The time for the whole system to reach consensus on the status of transactions through the mechanism like (PoW) of bitcoins will make the public chain to be slow.
Congestion sometime could be con to public chain if the number of transactions is very much on public chain, the processing speed of the transactions will certainly reduced. The blockchain is a very useful technology that helps for in storing and transmitting data of the issuers or investors which also have a lot of advantages such a traceability, decentralized, amplification and secure.