The speed sensor is included for a couple of reasons. First off, you still get speed even when not really moving, as on a trainer. You also get speed even with a poor lock or no signal at all (possible in a canyon). Lastly, if you do not need your position you can save battery power by turning the GPS off and just using the wheel sensor.

As for function, once I adjusted it all it works great. Cadence works, speed sensor works, the spokes clear the sensor, and all is well. The odd shaped chain stays did present a slight challenge, but at the worst you would just not have the speed sensor - which is not a problem except for maybe riding on a trainer.