Sometimes small issues are found during a review, like spelling issues and such. It would be nice if a reviewer could suggest an edit, instead of making a comment about the edit that should be made.
This shouldn't cost the reviewer any extra time, and the original author doesn't need to open his editor, switch to the correct branch, make the suggested edits, and commit his changes again. Instead, the original author only needs to accept or decline the edit, and can immediately land his commit with the edit included.