According parity.io website:
Proof-of-Authority is a replacement for Proof-of-Work, which can be used for private chain setups.
The chain has to be signed off by the majority of authorities, in which case it becomes a part of the permanent record. This makes it easier to maintain a private chain and keep the block issuers accountable.
PoA networks are well-suited to regulated industries where entities responsible for maintaining the network (authorities) need to be known, rather than remain anonymous as in mining-based chains like Bitcoin and Ethereum.
It is underlined to use
Proof-of-Authority for a private chain.
What is the reason? And Is it logical to use "Proof-of-Authority" for a "public" blockchain, in sense of keeping decentralization?