When working properly, the wheel sensor improves auto-pause operation because it's free of the effects of GPS drift and position noise. I set auto-pause to 3mph using a wheel sensor, but or 6 mph when relying on GPS. For the slower going mtb, I use two wheel magnets at 180 degrees so that the Garmin gets more frequent pulses. With two magnets, the wheel circumference is set to 1/2 actual in order to read speed correctly.