This can be very dangerous if you are following a car or truck. One reason I can think of is that if anything like a dead animal is in the center of the lane, the car or truck may not try and avoid, since it would pass over easily. And you would have no warning and may not see it in time to try and avoid. The tire trail is much cleaner anyways and makes for smother ride, don't you think?
I never ride center lane I like to be in the right hand lane, there is always grass or somewhere to swerve off to god forbid I ever need to.