Hi, What I mean is that you want your legs going 80-90rpm on the pedals, if you are in turbo and going slowly but putting more torque into the pedals, then the Brose motor is doing more work and it is also harder on the teeth on the belt. More torque from you + turbo (multiplies your torque by 300%) means much more stress on everything.
If you are going a higher cadence you are putting less torque in the pedals so the motor doesn't have to output as much. The middle setting also multiplies your leg torque by 100%.
Power is torque times rpm so if you are pedaling at 50rpm instead of 90rpm you need to put 1.8 times the torque into the pedals to generate the same amount of power. Since the e-bike motor measures the torque you are putting into the pedals 1000x per second and then multiplies it by some factor spinning at a higher rpm is not only better for your joints (especially knees) it is also better for the e-bike motor and belt. Does this make sense?