By default, the top (current) commit acts like a staging area and in fact is implemented as a dirty working tree in git.

Commits start live without a description, and can’t be pushed without adding one. jj commit names the current commit and creates a new empty, unnamed commit on top, which effectively is precisely git’s behaviour.

I implore you to try it. In practice the distinction just doesn’t matter, except it’s one less concept to keep track of, and jj allows you to make up other workflows if you want.