Other than the obvious "because I can", why would you need to do this? It is my understanding that it's the heat that pulls the moisture from the filament, so unless you are trying to heat the filament up more, I'm not clear how 2 heaters is better than 1.
I guess that will mostly depend on what you are drying in it. I would not use anything less temp rated than ABS/ASA personally. PLA will likely not work.