I never did Twitter so can't say what's different about Mastodon. But I have two accounts there for two separate main interests, crafting and gamedev.
On both of those accounts it's just a nice way to see what other people are up to within those topics, share my own projects, and generally meet new people and get into conversations around our shared areas of interest.
You can do that here on Lemmy too of course, this just lends itself better to longer in-depth discussions while Mastodon is better for more casual chatter.
I like them both and am happy with my life choices ๐
Complaining about it mostly