Personally I believe in Kaizen, even a small improvement is an improvement.
That said, a more concerning edge case is the improving of rubbish. When a post is incomprehensible, fixing 1 typo, 10 typos or 100 does nothing to improve the post or the site. The correct thing to do is reject edits small or large on posts that should be closed or deleted.
If an awesome post had a handful of typos and someone fixed them, I see notno reason not to approve the edit. Heck, it is easier than navigating to the post and doing so yourself.
I also totally back Jeff on his call to outlaw the 1-typo edit suggestion. The reason I agree with this is twofold.
You can do better, always. The edit suggestion system teaches you how to edit, and editing more that just one typo is a good practice.
Processing edit suggestions is not a free process, it cost eyes, distraction and time. We want quality in the queue, so high standards is a good first step.