It really depends on the ramp and what the ramp is made out of. If the ramp is dirt and rock the more people drive on their trailers the more just behind the trailers builds up and one day someone will it it with their prop. If you have good ramps then the drive on can make sure the boat is set evenly (or more or less) on the trailer. The float you can be off to one side or another and have to put the boat back in again to make sure you care center.

This year i have been having problems loading for some reason and let off the gas too soon so i end up about 2 inches to far back so i have to crank the last few to make it the rest of the way on. Talk about causing more work for ones self.