Occasionally I've seen (and even made) this sort of comment in regards to reading motley assortments of screenplays and films -- the premise being that in a film such as Voodoo Tailz you'll at least learn some ways not to make a film, or in reading the worst screenplays for a contest or company, you'll learn how not to write a screenplay.
I no longer buy into that theory. There are an infinite number of ways to write a bad story. Eliminating one of them still leaves you with an infinite number.
What you need to learn is ways to write a good story (or frame a nice shot). And that's why you should read even the bad screenplays or watch even the bad movies.
For instance, The Grudge, while financially successful has some serious story problems. However, it also has some amazing visual moments: a ghost floating up in the corner of a room while her impossibly long hair swarms down the walls. That sort of liquid image is something I've seen replicated in other stuff since then.
Tarantino has made a living off of seeing the terrific moments in less successful films then combining and using them in new ways.
Or the wonderfully budget-conscious Necropolis: Awakened, previously mentioned here. I'm still enamored with its idea that the zombie-king hires some hit men to come and take care of his pesky-protagonist hero-killing-all-the-zombies problem. That's just remarkably common sensical -- though, were I to steal it, I'd instead have it be the townsfolk ordering out for mob hitmen to come in and take care of a vampire, or similar monster -- something that they couldn't convince the government to take seriously but bad enough that they couldn't handle it themselves.
The reason this works is that everyone's got a few good ideas and if they write their one story, make their one film, or sing their one song, that's where those ideas end up -- well, except for Voodoo Tailz.