The feedback intensity affects the resistance you feel in your trainer. For example, if you're on a slope of 10% and the feedback intensity is at 100%, we'll send 10% slope to your trainer to simulate. If the feedback intensity is at 50% then we'll send half of the slope, so the trainer will simulate only 5% slope. This was added after our first route, Stelvio Pass, was released and people were having a hard time climbing it. By default we set the feedback intensity at 42%.
Feedback intensity has no impact on speed.