Niche communities are what made Reddit fun/useful to me. It was really nice to have discourse with a community that liked the same video game, movie, hobby, political ideals, etc, that you did.
Guides and tutorials were the other big thing. I utilized and contributed guides on Reddit regularly. It was really nice to engage with a community to solve an issue rather than use some AI generated or ad ridden article.
I hope to see Lemmy fill these gaps and it seems it has the potential to do so.