I think the main thing about instance being important is the instance moderation and federation choices. Some people will of course want as hands off as possible, but some instances are certainly not that (one is very explicitly communist for instance IIRC). So ideally you'd pick an instance that fits your moderation goals, followed by one that you have some other affinity for - like the gaming idea. I joined sopuli because of it being Finnish and I have that heritage, even as an American. I also like not having everything hosted in the US so...

I could also easily see some people having multiple identities tied to instance interests. I suggested it would be nice if /r/sysadmin here at /c/sysadmin was not a community on lemmy.ml but actually its own instance, perhaps trying to pull in /r/networking, /r/sysadminjobs, /r/linuxadmin etc. Not only is that more likely to be work related, so you want a "work" identity, but it seems like you'd have the benefit of a group of communities filling the frontpage of the instance with stuff you're likely interested in.

I see this a bit with mastadon with a journo.host vs an infosec.exchange vs my generic vivaldi.social account.