It's best to not turn the bike on and off while moving. Doesn't hurt anything mechanically, but the sensors (cadence/speed/power) need a zero setting. Again, doesn't hurt anything but you're more likely to run into an error of sorts.
Riding the bike fully turned off versus "on" with no assist, there is ZERO output from the motor while at zero help with the system still on reading speed/power/cadence.
I think most folks, understandably, don't realize how heavy duty these bikes are spec'd compared to acoustic bikes. The tires are really heavy and flat resilient, and the bike weight is significant especially uphill or stopping starting. Also keep in mind the best part of ebikes is the fact that you can ride in a super upright position, which is VERY un-aerodynamic, and still ride longer distances. When you're upright on these bikes it's like riding with a parachute attached, look at any pro cyclist from a side profile. Back is usually flat with is very aero, combined with an aero frame and deep section wheels. I've tested this myself riding to the shop, I'm usually laid down on the bars in an aero "tuck" of sorts and I can sit at the max speed with assist only putting out about 170-200 watts.