I use them for a couple of reasons. Arrows are easier to find and see with the wraps on which helps on the range or after a shot on an animal (this may depend on color as well). My Blazer vanes stick to wraps extremely well, so I like using wraps for that reason. Also, by just sticking a wrap on, it is easier to clean your arrow to replace the wrap. You only deal with sticky stuff instead of dried on glue you have to scrape off and risk ruining an arrow.
Disadvantages - adds weight to the end of your arrow decreasing FOC (not much usually and depends on wrap length). If you mess up a vane, you pretty much have to replace the entire wrap and fletchings unless someone has any tips on this.
I shoot a white 4" wrap on my arrow. Decreases the weight on the end of my arrow compared to the longer wraps, but still increases visibility.