I could have sworn that I'd posted on this thread - I think there are multiple threads/versions of this conversation going on. This is a very important issue for me, too. As others mentioned above... this is used A LOT by students to submit work in file types that I don't want them to use and/or to submit work after deadlines have passed.
If I had the option to simply disable comments on assignments/quizzes altogether then we'd avoid so much trouble for me and my students (not to mention my TAs/graders). If students can just attach anything they want to attach, in any format they wish, in a comment at any time they feel like it then there is no reason whatsoever to be able to restrict file types for assignments or to even have a deadline at all. If they can, then they do, and since they were able to then I "MUST accept the work...", "is part of the social contract" according to student conversations I've overheard in the hallway recently.
If a student is having trouble with preparing work in the file types that I have the system set to accept then they need to contact me or a TA to discuss and get help learning how to prepare their work - not just avoid by submitting whatever via a comment attachment.
If a student is in a situation in which they are going to miss a deadline for a legitimate reason then they need to discuss that with me, not just sneak it in later in a comment. I typically even go along with a bad reason for missing a deadline the first time it comes up... I've had a few in emergency rooms and hospital rooms unnecessarily stressing out about trying to finish up and submit as soon as possible after a deadline via the comments when I'd have been happy to allow more time after they left the hospital. If they had simply been unable to submit late and knew they were unable to submit late then I'm sure they would have contacted me to discuss - I was often contacted in situations like this when my institution used Blackboard because there was not really a good way to sneak in late work like this.
I am also really feeling like there are too many different avenues for conversation that I don't have control over so students and I are actually overwhelmed. I need to be able to streamline conversation options in order to reduce confusion. Graders leave feedback in grading rubrics. That is really all I want going on in assignment submissions. It is too easy to miss a notification setting (I manage nearly 800 students, 30 TAs, in multiple courses with multiple sections each semester) and not get notifications about different comments, etc. I need students to ask questions to TAs during class, email after class.
I am able to disable student comments on announcements (which may have a place but seems very unusual to me in the first place) so I'm not sure why not be able to disable student comments on other things such as assignments/quizzes...