I don't think I ever blocked anyone on reddit, but I've been pretty block happy on lemmy. Mostly because it's a smaller community. With reddit, it was easy enough to unsubscribe from the big popular communities and focus on my niche interests and rigorously modded communities like askHistorians. That way I mostly saw stuff that was genuinely interesting to me. And if someone was annoying, they were just one voice among thousands.
Here on lemmy, there's not enough activity to be overly selective, and I actually enjoy the casual vibe of asklemmy, showerthoughts and nostupidquestions. While I'd never visit their reddit counterparts, here the community is small and it feels more personal. But this also means that there's the occasional poster who I'd rather just not have to see. So, to keep my time on lemmy enjoyable, I block them.
I don't really think it's a big deal, I don't even think it's a criticism of those posters. It's really just that the content of their posts / comments are something that doesn't add value to my experience. I've blocked well-intentioned, but obviously teenage, users because I'm not interested in their personal life questions (but they're entitled to ask!); I blocked someone just for posting too many moth memes when I was getting sick of that fad.
I'm pretty sure I've never blocked anyone for disagreeing with me or my beliefs, but if someone seems like their trolling, or simply has such poor social communication skills that they are coming across that way, I'll block them. I generally look at users history and check if I'm likely to miss anything in the future. But invariably, the type of user I consider blocking generally has a bunch of dumb, negative or uninteresting comments and posts.