Yes. Adjusted with a servo. Thing is, if your engine goes lean in the air, and you don't have it, goodbye $160 piston and cylinder, and maybe goodbye airplane. Plus you can do stuff like lean it out for a little extra performance on takeoff, and richen it up again for the rest of the flight. It has saved me many times.
Pipe pressure versus fan pressure, big debate, but either one works. I have used both, have no real preference.