Like? This isn't explained, I'm curious on why I would want to use it, but this is just an empty platitude, doesn't really give me a reason to try.
You can do all that in Git, but I sure as hell never did; and my co-workers really appreciate PRs that are broken into lots of little commits that can be easily looked over, one by one.
With `jj new` + `jj squash`[2], you're collecting work that you can review as a separate thing anytime as you go along. You don't have to remember anything. If you throw in an unrelated change, you'll notice it if you review the changes before squashing them, so you can split it out then. And I'm pretty much always working in this state even when I'm at the top of my branch, so `jj new some-deep-node` doesn't really change anything. If I get called away and have no memory of what I was doing when I return, it doesn't matter: my jj state tells me exactly where things are and what I was doing.
[1] Which is not a huge problem, you have deferred conflict resolution so if something goes wrong you can probably just repair it with normal editing or your editor's undo functionality.
[2] I don't usually bother with `jj new -A`, since I'm going to squash my "out of line" temporary commit into the linear chain anyway. `jj new -A` is more similar to `jj edit` than `jj new` -- it shares some but not all of the modal disadvantages. So perhaps my answer to your actual question is: "yeah, I dunno either."