What is recommended for edits?
Anything that substantially improves the post:
If you are going to edit a post, make sure you’re substantively improving it. Avoid making isolated, trivial edits, as they are the source of much friction. For example, don’t bother changing “its” to “it’s” unless you have several other edits to make in the same post. There has to be a legitimate case that your edit made multiple changes transforming the post from good to great — or at least substantively improving it.
(Except when you happen to be editing that rare “perfect except for this one misspelled word” post. This is obviously OK to edit. In my experience, the type of posts that really cry out for editing need a lot of editing to be whipped into shape.)
So don't ever be afraid of doing too much - worry about not doing enough!
If you see a poor edit, fix it - by editing! - or roll it back. Post owners are notified of edits, and can roll back changes they don't like with a single click (there's a "rollback" option under the post for owners after someone else has edited it).