I've been wondering for a while why there is a minimum (6 letters I believe?) when I need to edit someone else's post. Most of the time I don't have any problems with this but in cases where the OP has a spelling or punctuation error, I won't be able to fix it. I don't see any reason to include a minimum of 6 letters in editing other people's posts. What do you guys think?
In general, edits are supposed to add value, not merely make minor corrections to fix typos or such. Very minor edits—those that can be made in less than the minimum number of changed characters, for example—are discouraged. One of the reasons for rejecting an edit says:
This edit does not make the post even a little bit easier to read, easier to find, more accurate or more accessible. Changes are either completely superfluous or actively harm readability.
It’s going to be somewhat subjective whether, for example, fixing typos or missing punctuation or other minor formatting issues is making the post “even a little bit easier to read” vs. “completely superfluous” but very small edits are vastly more likely to be the latter. (If you could figure out what the author meant, other folks probably can too, so you’re not really making it that much more readable....) To encourage people to look beyond just the missing comma or misspelled word for something more substantial that can be improved in the post, SE imposes the limit on how much has to change before a suggested edit can be made. So ... do that!
There’s almost always more to fix than just the edit you first thought to make. Any time you’re making an edit, you should be trying to improve the post as much as you can without changing the author’s intent. Using clearer wording, adding details found in comments that haven’t made it into the post, and the like can all make good edits, and give ample opportunity to make other minor edits along the way. Conversely, if you only saw one glaring but minor error that you. just. had. to. fix... look for other edits to make as well; there’s almost never just one thing that could be made better, clearer, or more nicely formatted.
See also this answer for more on why the limit exists and what you can do instead. Note, too, that with sufficient reputation you’ll no longer face this restriction—but that doesn’t mean trivial edits are suddenly okay.