I have seen bucks of all sizes use them, but believe the bigger the scrape, the bigger, or more dominate the buck was.
Doe pee's in a scrape then walks off leaving her scent trail, bucks check scrape and get on her trail. Kind of like a deer community "post it" board STS.
Same principle as using a hole in the ground filled with used cooking oil for bear. Bear gets in it and carries the scent for miles as it walks, then any bear crossing the trail, will follow the scent back to the bait.
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