To me the main difference is that there is no staging (so no stashing needed), and conflicts are first class citizens. In practice this means that you can usually halt your work halfway, switch a commit, rebase everything onto head and continue working even if one of the branches off your commit has conflicts. In git you would have to resolve those before the rebase can finish.

Since conflict resolution these days mostly boils down to “hey LLM, resolve conflicts” this is much nicer.

Also jj tracks every change to the repo so undo works much better and is more readable than reflog