So-o-o?

I'm with Richard Hammond (the hamster) in wondering why some people make such a big thing out of coming out, or others coming out as gay.  Why are we so hung up about a person's sexual preferences?  I have many friends (believe it or not) and for the most part, there's plenty of things I don't know about them - I don't know their heritage, or their religious persuasion for instance, and I wouldn't think they would see any need to tell me these things.  So why would they see the need to tell me that they're straight, gay, bi or whatever?  Is it because knowing where a person stands on the sexual spectrum can avoid awkward social misunderstandings - or rather not knowing can involve you in such misunderstandings? Only reason I can think of.