I do the same thing, never have a balance, and I am getting lots of frequent flyer miles. However, this is only a good idea if you are wired a certain way. For some folks it can be a slippery slope to heavy high interest debt.
It's not a judgement on anybody, but you have to take an honest look at yourself and see if it is a dangerous move for you or not. I know it sounds weird, but I have a real sense of accomplishment each month when I pay the cc balance in full. I know that I am living within my plan.