That's kind of the point of using them though. The goal is to -stop- saying "you either fit into this gender binary, or you are 'other'".
It's kinda like normalizing the use of "partner" instead of "husband/wife" even for the straight married people; it helps normalize relationships that fall outside of monogamous, state recognized marriage, and doesn't force gender definitions (what if you're in a committed relationship, or married, to an NB person?) or force releasing sexuality just to indicate you're in a relationship (i.e., the person maybe doesn't want the fact they're gay to come up in this setting).
Providing your own pronouns, even if you're cisgendered, is a form of allyship; you're normalizing it, and helping create space for those whose pronouns don't match how they present to provide theirs.