"What those guys said"
I've been waiting a long time to say that. I especially agree with what Ryan said.
I'll try to add to what has been said. First of all you have to think about what kind of country whitetail deer evolved in (large mature forest) and how many deer there were. There were a lot less deer a few hundred years ago, plus the travel corridors, bedding, feeding, staging, loafing areas were not restricted by agriculture, cities, subdivisions, etc. They did not just trip into each other. They had to find a way to communicate/leave messages. They could not speak and they could not leave a post-it note on the fridge. What did they have to use for communication? They had scenting and visual capabilities. Scrapes primarily fall into the scenting category and rubs fall primarily into the visual category. As the whitetail deer is bebopping through his hood he wants to let his posse know where he hangs out (visual/rub line) he also wants to let the girls know who he is (scent/scrape).
There are other things that go on at these two areas that we probably don't fully understand yet. Like one of the guys above said he saw a buck rubbing out of pure aggression. I tend to think it is out of sexual frustration. I saw a little six pointer work on a series of saplings for over an hour and his velvet was gone before he started. I've seen does scent check rubs. I've seen does urinate on a scrapes, paw around in them a little, and scent check the ground and tree limbs that are above the scrape. These are a few examples of communication but what else might be going on.
These are some of the reasons I love whitetails. I like to study these mysteries and then I really feel fortunate if I see for myself what I've studied. Or if I see a strange behaviour that I haven't seen before I like to go and find out why that behaviour is there.
Sorry I got a little long winded there.