I grade a lot of essays, but I believe this feature might be valuable for other disciplines as well.
Canvas currently has the ability to post comments in video (webcam) or audio form--though, the flash programs for these seem to be hit or miss for me.
For essay feedback, I want to be able to communicate what I'm seeing in a student's essay, but I don't necessarily need them to see my face. Far more valuable to me is to be able to point to aspects of the essay or assignment while I'm talking and to have the student see those specific aspects while they are hearing my comments.
I do this now using Camtasia. I open speedgrader and begin recording a screen capture with audio. I then have to save the file and upload it to Canvas using the media comment video upload option.
This works, but it is a bit clunky. My speed at grading would be greatly increased if I could press a button and simply begin recording the screen.
Again, I know the benefit of this with essays, but my guess is that it could be of benefit to almost any discipline. If an instructor is taking the time to record a comment of any sort, it is probably a comment that has something to do with the digital object that is right on the screen. The added benefit would be that if the recorder is capturing the screen and not just the current window, an instructor could use the video as a digital whiteboard. I can imagine a math instructor giving a just in time KhanAcademy style explanation for a problem on which a particular student seems to be having difficulties.
Since I have an android tablet with a stylus, if this could be incorporated into the android speedgrader app, that would be some wicked awesome future s%&t!!!