Why are the limits equidistant to 0?

[ezickler]

I'm just learning about PIDs and the implementations, as I might want to use it to control the temperature of my coffee machine. In that scenario a PWM signal would control the heater. So a negative output wouldn't be that useful here. I also imagine this would be true for many other applications. So isn't it quite limiting to have the limits always equidistant around 0? Of cause one can map the PID output from the "-limit to limit"-rang to the actual one but that doesn't seams that convenient.

I get the it is quiet intuitive to have positive output from increasing the input and negative for lowering it, but this seams also quite the special property for a system.

Is there some other reasoning for having the limits this way I missed?