I'm with the majority here - edit to improve spelling, grammar, clarity of intent etc where appropriate…
… but …
Limit it to new posts only, unless you can make significant improvement in other areas at the same time.
An edit brings a post back to the top of the Active list, so a lot of insignificant edits on older posts skews that list - which is [imo unfortunately] the default view when landing here.
There's an element of self-control needed when editing older posts, because of this promotion to the front page. If you're going to systematically check & edit posts you read, be sparing. One or two every so often will aid the site without swamping the Actives.