It does seem like some servers have specific niches, so if you're really interested in a specific servers niche using that instance would prevent you from having to sync those communities with your instance.
I think you’re right! It can be nice to have an active local feed with topics you’re interested in, so that’s a good reason to pick a topical instance (eg mander.xyz or slrpnk.net).
Nobody asked my opinion but my interpretation of how this whole fediverse "should" work is that while there can be empirical instances, federation shines with smaller, easy to manage instances thst connect to each other.