I emailed Csats for a definitive answer on whether or not the comment boxes are requirements, and they ANSWERED!
"Lori, great question! As you noticed, we may alternate between the two comment formats (a comment box below each question, or just two comment boxes at the end). But in all cases, the comments are intended to be used for if/when you have something specific to point out. Your example of a surgeon repeatedly drawing the needle without making a stitch is a perfect example - it's the kind of feedback we would send directly to the surgeon themselves.
When you're able to be specific like that, it makes the feedback more valuable to the surgeon. As you noted, 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.
Hope this helps.
C-SATS Support"