I think everyone uses jj a bit differently. Personally I don't like having a staging area; for me it's an opportunity to forget to add a change to a commit. I don't keep files in my work tree that I'm not going to commit or ignore.

But when I first moved to jj I tried to make it work as closely to git as I could. The model I used back then was to have a commit that I meant to upload eventually, and then a working commit on top of that. Then `git commit --all` was `jj squash` and `git commit foo bar` was `jj squash foo bar`.

Eventually I got lazy. It was an extra command, and I almost never have the situation where I don't want to include a file. In the rare case that I do, I'll create a new commit with `jj new` and squash that file into there (you could have a shortcut for it, but the long form is `jj new -m "foo changes" --no-edit && jj squash --to @+ foo`, and then keep working.