Currently, when we switch from To-Do to In Progress, we get a box asking for a comment. I think this is unnecessary, but not a serious problem.

However, we do not get such a box when we switch from In Review to Review Complete, and here I think having a comment box is highly desirable: I virtually always want to make a comment when I complete a review, and I'm assuming doing it in a pop-up box cuts down on unnecessary notifications.