How important are resv at campgrounds on Alaska Highway

We have driven up and back twice and had reservations for every place we stayed. We were glad we had them because that is the way we like to travel. However, I think I only remember five or six campgrounds, on both trips, that were full. I was very pleased to find that the vast majority of campgrounds in Canada and Alaska took reservations using your name and phone number. They didn't require a credit card or deposit.