I use a combination for 2 reasons:
1. I have small hands (I can reach shift & 6 at the same time, and ctrl and 5 if I stretch but nothing passed them)
Just trying to figure out how this one is relevant.
I have every single one of my abilities, including ones that I would never use, along with stuff like seeker droid, speeder, medpacs, bound with just the left half of the keyboard and shift + the left half of the keyboard. I don't have anything as far as 6 bound with shift (don't have shift+5 either, actually), and I don't use ctrl for anything.