Also, for whatever my purely anecdotal experience is worth, I'd say the general quality of a professor's teaching was negatively correlated with how hard-ass they were about anti-collaboration policies. That also held true for a couple classes I'd dropped and retaken with a different prof.

One might think I'm just rating easier professors higher, but no, there were definitely enough sub-par teachers with lax policies and forgiving grading who failed to impart what their course was supposed to cover. There were also tough professors I learned a lot from. It's just that I can't recall a single decent instructor among those obsessed with anti-collaboration policies.