There's lots of stop lights that won't change until a car is over the magnetic sensor. This means staying stopped at the light on a bike will never get you the green (until some car pulls up anyway, but where I live that can be a long time).

You can get around this sometimes with a bunch of strong magnets stuck to your lower bracket, but only sometimes and it depends on the sensors' calibrations.

Point being, this change does have some practical benefits if you have to deal with such traffic lights - running the red in sight of the wrong cop is no longer a concern.