I think if you are relatively weak in the pull compared to in the squat, heavy snatch/clean deadlifts in the right doses are very very useful. I have personally found it to improve my classic lifts greatly. For people who are naturally good pullers (people who can regular deadlift 115%+ of their back squat) it's probably a waste of time.

http://www.teammdusa.com/coach-pendlays-blog/the-role-of-thedeadlift-in-weightlifting

The lifters who need the deadlift are usually the ones who are the worst at it. Most lifters who are gifted at the sport of weightlifting have torsos that are longer than average for their height, and legs that are shorter than average. Having a long spine puts a lifter at a leverage disadvantagege when pulling a deadlift off the floor, especialy if it is paired with shorter than average arms. Jared Fleming is one such lifter, Donny Shankle is another. Both were great at the squat, and terrible at the deadlift, simply because of leverge. For the average person, the squat should be about 10 to 20% below the deadlift. Jared and Donny can both squat more than they can deadlift, something that is quite rare...These lifters can often improve their lifting dramatically with moderate training on the deadlift...

On the other end of the spectrum is a lifter like James Tatum. He is taller with more of his height is in his legs. He also has longer than average arms. James is a very good deadlifter, and like many lifters built like him he can deadlift much more than he can squat. Most lifters built like James can do so, and doing extra training on the deadlift is not usually going to help their lifting much, if any.