Superior grip of the string. The absence of the wood beneath the strings really allow you to grip well and bend easily. It also allows you to do really wide vibratos. But it does hurt the fingertips at first as there isn't any support and the string digs right into your flesh.
It'll set you back at least 300 plus to scallop a full neck. Prices are dependent on the no. of frets to be scalloped.
There's an online tutorial at
www.projectguitar.com on how to scallop a neck. It's a very time consuming process that involves quite a bit of work. Gotta be careful as well.
Be forewarned scallops DO weaken a guitar neck, making it more susceptible to more problems if not taken care of properly.