Do you want/need medication? If so, an official diagnosis will help. If not, it's probably not worth it, unless it's going to put you at ease.
In my case, official diagnosis really fucked me up for a while, as I could no longer deny the things I'd spent a lifetime denying/ignoring/making excuses for. It made me feel broken in a way that can't ever be fixed.
Eventually, I got over that, as I realised I and everyone else is "broken" in a thousand little ways, and I was placing way too much emphasis on one aspect. But, still, it took me a while to get to that point.
Given that I don't really use ADHD meds (adult ADHD is very gatekept), I'm not sure formal diagnosis has done much to help me. But aside from the initial burst dam of negative feelings, it hasn't done much to hurt me either.