A film class needs film. Duh. Close-analysis of film clips is an important part of teaching sections, and nobody wants to mess with scanning DVD chapters to find the right clip. So most TAs I know make clip reels — DVDs of clips — to show in class.
I was interested to see that the Society for Cinema and Media Studies has issued a statement of best practices for fair use (the doctrine that covers this area of copyright law). As far as clip reels are concerned, SCMS has this to say: