Well, the only real benefit is that each individual level can be put onto a different controller or can be set using the Herpstat Pro to a different temperature which is what the OP was asking for in the beginning. If all the flexwatt is running to one plug they would all be running at the same temperature.
To ThyTempest: if you know, say, that you're only going to need 3 levels for corns and 3 levels for balls then you could either zig zag or daisy chain those 3 levels together which would be easier than doing each strip individually.