I think it is worth mentioning the Editing section from the The Complete Rate-Limiting Guide:
- 5 edits on one's own posts per day, more for high-rep users (scales with reputation), does not apply to ♦ mods
You have already edited 5 of your own post today; further edits are
not allowed until tomorrow
5 deleted old answers per day (not sure if this is counted along with edits or separately, confirm/refute), does not apply to ♦ mods
At most 5 pending suggested edits per editor (20 on beta sites)
- Unregistered Users can't suggest edits on posts < 10 minutes old
- Users with < 10k rep trip Captcha if more than once per 30 seconds, or faster than 5 seconds after starting edit
- Users with > 10k rep trip Captcha if more than once per 10 seconds, or faster than 5 seconds after starting edit
- You can only save a tag wiki edit once every 30 seconds.
The only other editing "limit" that I know of, mentioned in a comment by @whuber, is that a flag to moderators is raised when a question has been edited more than 20 times. I have not been able to find this documented but I think it is there to detect users who are performing trivial edits to bump their question to the home page. Such behaviour can be met with suspension, but here at GIS SE, as far as I know, we have always clicked away that flag, because in all instances that I have seen the edits have seemed reasonable (usually on Community Wiki posts).
I think any editing that improves, even quite modestly, the chances of a question being answered or acting as a better example for questions by new users (so they get theirs answered quicker), is worth doing.
The edits to avoid are those which strand/invalidate an answer by changing the question (that has already been answered) too much. Those edits should be rolled back and comment made to suggest that a new question be asked.
Remember that Q&A is not designed to be a discussion between askers and answerers on how to solve a problem. On the other hand askers can get great insight into how to solve their problems by asking focussed questions that break larger problems into answerable chunks (in separate focussed Q&As).