Well you can use the amount in there as a gauge but it really depends how much you start with. I use flexwatt belly heat for all my snakes except my GTP so i dont use a lot to begin with. And with Caesar, he takes tsunami pisses so i end up spot cleaning about a 6-8 inch 'impact' zone with each big piss.
If you enjoy doing the cage cleanings every month, then go for it. The only thing it could hurt would be your wallet. It definitely wouldnt hurt the snake at all to have a nice clean cage all the time.