my boys have kinda medium hair, in my opinion. I use a 7 in the summer and 8 or just scissor in the fall/winter. I don't blow dry them simply because it is more fun to watch them dry themselves
their hair doesn't mat, it actually comes out very soft and wonderful to pet and run my fingers through. I try to brush it while it's damp or they get twiggies, but other than that, I see no reason to fuss with the blow dryer.