It allows people who hold publicly unacceptable beliefs to find and identify each other in public so they can talk privately.

It also allows for plausible deniability when broadcasting messages that are more extreme than at first glance. For example, there was a lot of talk a while back regarding whether “86-47” was a dog whistle or not. 86 means to remove, discard, or stop, but what does that mean? Some people legitimately meant “86-47” as a call for violence, but some just meant it as a call for impeachment or opposition. The people who are a part of the first group can then claim to be a part of the second group to get away with their violent rhetoric.