I've dog-eared early on in my short window cleaning 'career', so didn't know much else. But recently Wor Lass and I used brand new 'undog-eared' channels and within two days I dog-eared them.
It definately helps reduce scrimming; sometimes to a level where you don't have to scrim at all; depending on the window and frame type.
I'm not sure that it wears the rubber out quickly (as Squeaky suspects it might), and even if it did, it would be worth it.
We like to change our rubbers regularly, they're cheap and a new rubber helps you to work faster and therefore you earn more for your time; less frustrating too.
I use a 14" inch squeegie; does size matter with dog earing?