Sure thing. Recently, you've probably noticed the "OPTIONAL" tag above most of the comment boxes. Obviously, those are not required, though they are appreciated.
In general, the comments are intended to be used for if/when you have something specific to point out. Maybe you saw the surgeon drop a needle or burn something - that's not something that would get captured in the 1-5 scale. A useful comment like that will get passed directly along to the surgeon themselves for their review! We very much value thoughtful comments like that, but don't expect you to write them all the time. I think eventually we'd implement a bonus system for reviews that leave useful comments. But to be clear, saying "great efficiency overall" when you are giving them a 5 isn't very informative, and you're welcome to not bother saying anything in that case.