Is that actually desirable or just growth for growths sake?

It's actually desirable. Without subs on more topics (which should also mean people discussing those topics), Lemmy is not a viable alternative for the people who want to focus on content. And this is particularly relevant for more niche subjects because of how the scale of conversation works. I should know. I created two communities (technically magazines on kbin, but same idea) but until people come to them, I'm mostly fully just waiting there, fingling fingers.