`edit` is still useful; just, for ..editing (!) something, instead of viewing it.

If you have some unfinished changes at the tip and want to temporarily checkout something 2 weeks ago, you `jj new` to there (similar to `git stash; git switch whatever`), and then later `jj edit your-old-tip` to go back (equivalent to `git switch main; git stash pop`; I think `jj edit` being an extended replacement for stash-popping things is a reasonable way to think about it). (and if you don't have any uncommitted changes, you always `jj new`)

jj also has a concept of immutable commits (defaulting to include tagged commits, and trunk at origin, which it'll disallow editing as a layer of defense)