It drastically simplifies the process.

Redescribe, reorder, split, squash, abandon commits is trivial.

Auto-rebasing is fantastic, fix a conflict once and not have to keep correcting.

You can rebase individual commits, ranges of commits, etc. You can also rebase trees I.e. forking branches with a common ancestor, with a single command.

The operation log also makes it feel super safe. You can always undo a jj operation or restore to a past state