On my heavy bikes, if I pedal hard from a start (difficult to do with my knees the wya they are, most of the time), and don't hammer the throttle, I can bring my typical Wh/mile down from 29-35Wh/mile to 27-33Wh/mile, for a 2.5-mile ride with about a dozen complete stops and starts. That is even if I do not pedal past about 7-8MPH, just doing it to help get started, then use the mtoor only from there thru 20MPH where I cruise.
Naturally, I don't do this except to test things or if I am riding a very long way and think I might need the range.

Mostly I hammer the throttle on startup and keep it that way till I am up to speed, cuz it's easier.
So yes, pedalling can help a lot, especially if you have lots of full stops.
As others noted above, it also can make a big difference to the motor power usage, but that depends on how your setup is made, and the speeds you ride. If you are riding in the inefficient speed zone of the motor, then pedalling will make a lot more difference than if you are up there in it's efficient zone.