We used to do this when I was in college in the early 70's (went well with the hippy culture). It can be difficult to control, as F/1.4 points out. It can also be fun and isn't for everybody, but it can teach students a lot about exposure and development and how the chems work.
I would also put the paper up last, as pointed out, don't know why he feels he has to focus on the paper.
I don't remember it being a technique which lasted very long with anyone.