I had the perfect use case for something like this last year.

I wanted to make a (very) short movie with a similar feel to Waking Life, except instead of rotoscoped images I just wanted to do varying degrees of edge detection on each frame. It came out looking pretty good but it took a lot of tweaking individual numbers in a python script and repeatedly rendering the same clip before I could even get a set of choices to decide between.

Having something like this with me when I was filming it would have made a huge difference!