I like it to keep track of communities that don’t have enough members here to be very active. I don’t participate in the discussions, but it’s good in case some news come out that I would miss otherwise.
Lemmit.online is also good, because it actually lets you know that it’s mirroring reddit. There was another instance that was mirroring reddit including comments, without any indication. I started “participating” in the discussions until I caught on to the fact that I wasn’t getting any answers or up- or downvotes because it was just full of bots. It soon landed on my blacklist.