One possible benefit of general communities is that they provide potentially alternative distribution and rewards rules (like VYB's no downvotes). While that particular attribute might not end up being such a great thing, in theory, experimentation should ultimately show what works best. In that regard, the more general communities the better (provided they are doing something different). Eventually, people will migrate towards what works best. In theory. I suspect that there is a limit to how many general communities can provide meaningful rewards so it's not like a 1,000 of them could pop up and really survive (or thrive anyway).
Plus there are only so many tags you can devote to general communities. If you aren't posting to a community related to the topic you are posting and/or tagging your post with a couple of relevant tags, I think it is to you detriment. These days I mostly find new people to follow either because of reblogs or from the list of recent posts I get in communities or tags I post in. If you are making those retrogaming posts but only tagging them vyb or pob then there's a 99% chance I'll never see it and you'll lose out on at least one vote...