Well it is kinda important to tell people
Like with both attraction and gender that’s just something that it’s assumed you’ll go along with.
For gender, it’s necessary because it could mean people calling someone by a name or pronouns that makes them more comfortable, or getting access to gender affirming medical care.
For sexual and and romantic orientation, it is always irritating for people to assume you like a certain gender, only a certain gender, or any gender at all. It makes people more comfortable.
Unless the people they come out to are bad people, then it’s very uncomfortable.