Focusing on the bare ground glass on the other hand is influenced by your sight. If your sight is not the one which is presumed to be by your viewfinder (normally 0, sometimes -1 dioptre, it's indicated in the camera specifications) the entire focusing system will act as a correcting lens for your eye, and the best focus for your eyes will not coincide with the best focus on the film plane.
Yes it will. Best focus for the film plane will coincide with best focus for your eyes, it just won't be as good as it would be with perfect sight. It can only get more out of focus either side of the in focus point.
"People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.