Pronouns are just your preference for what you should be referred to. If you don’t provide them people will assume. The logic is that if only people who want to use specific pronouns suggest them, you are essentially outing yourself so even if you associate with your birth pronouns, it’s polite to present them so it’s less awkward for others.
The actual use is more awkward. The expected use is that you use it when the person in question is discussed but a pronoun isn’t really used unless that person is not around so again it seems to just be a polite way to present yourself.
For added context a good use case of announcing pronouns would be a research paper where someone would be described to another person Edit: Ive been made aware about another obvious use case. Talking to people online where you might not have a way to identify any other way