Value is of course subjective, but many of jj’s popular features, like undo, are based on this.

(I actually think it’s tremendously valuable for a number of reasons but it’s fine to simply disagree about that.)

Additional complexity ? jj just increase the frequency of snapshots. it does not fundamentality the complexity of the system

The one thing I do like about git’s staging area is that it’s truly useful for reviewing a bunch of changes (bulk actions or automated tools). Go over the change chunk by chunk and stage what matters (magit makes that extremely quick.

That could be probably done by jj. But the git’s way is already fine for me.

Yes, jj does make this very nice and easy. It’s the same idea as git, except that “the index” is just another anonymous change, not a distinct feature.