Having been a teaching assistant who corrected programming assignments (and also a student), I always wondered how many of the students would read my comments, would go back to their solution and actually improve it. Probably none. If I (as a student) received a comment about a solution I submitted two weeks ago, I often didn't instantly know what the corrector talked about. I had to go back to look at my code. I'm not sure I always did that when I was busy. Additionally, I think even if I acknowledged the comment, I wouldn't actually go ahead and fix my solution.
I'm taking the scala course right now, and when I submit a solution and something is flagged, my thoughts are right in the code, I still have all the files open in vim, sbt running... so I can instantly go and fix it. And there is a real incentive to do that, because my score will improve.