Both, viewers and moderators can avail the public chat functionality.

fig 1: public chat option as a communication link between viewers and moderator

But only a moderator will have the ability to clear public chat,

To clear public chat:

Click on the hamburger menu visible just opposite to “Public chat”,  select “Clear” as shown in fig 2

Now a message appears on public chat which says that it had been cleared by the moderator

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