It depends what the motivation for "defining yourself" is. If you are looking for shared experiences with others to organise and fight oppression then yes, absolutely. If you are looking to create an "in group" with the goal of either elitism, enacting oppression or denying reality to uphold some irrational worldview then no. I think those two are easily distinguished in their results and intention though, which is why it's clear that feminists are right and GCs are wrong