Coaster, the main benefit is that you do not have to add any extra yeast! And the old dead yeast left over, will act as nutrient for the new batch. It's a great way to do things.
I also do this with beer, but after about 3 batches on the same yeast, and they start to mutate into something you don't want. At least beer yeast does, and I've never taken a wine yeast past 2 runs.