With the damper and fan in place I dont really use the fan full time for low and slow cooks. I set the fan to be "On at Max Only" and leave it set to run the full range of speeds (or from whatever low end speed where your fan actually starts to spin to 100%). With this setup the fan will blow when the pit temp is way low, once the pit temp gets close enough to the setpoint for the blower speed to move from 100% the fan turns off and the damper starts to control the pit on its own with natural convection.
If I am doing cooks in the higher temp range I basically reverse that setup by setting the servo to "Full open/Full closed only" and remove the check from the fan "On at Max Only" allowing the fan to blow all the while. This way the fan is pumping more air to feed the fire and hit the higher target temp and aid in quick recovery from lid open, the damper is there to close off and tamp down the fire if there is overshoot.
That said, with a servo damper, blower and Heater Meter there are many different ways to run your pit. You have to decide what works for you and your pit best, I prefer the above basic methods because I like the pit to run on natural convection air flow for low and slow cooks, and I like the pit to have fast recovery during higher heat cooks. This setup also works very well if you just let the blower and servo work all the time (do not check "On at Max Only" or "Fully open/Fully close Only")
PS one of the reasons people limit the top speed of the fan is because on some pits a fast blowing fan may stir up ashes that might get on your food. If you don't have that problem letting the blower run at 100% shouldn't be an issue....
