Pedalling is the most comfortable form of cruising. My e-bike is 2,000w and i regularly cruise at 30-45mph, but i still pedal.

There are two main reasons for doing so;
1) The pedals activate the motor. When i stop pedalling i have to use the throttle, which is less comfortable.
2) I say less comfortable because pedalling is the most comfortable way to sit in a sustained manner. You get reduced saddle discomfort, and keep a symmetry - remember, not pedalling, your legs are in two different places..

Obviously i don't put any effort into it. If i don't want to. Sometimes i do, just because i'm a 'push forward' kinda person. I run up stairs etc, so i like to be active. But still, pedal assist is the most natural and comfortable way to use an e-bike.