Well, there will be more force on the bearings by pushing the wheels out further. The bearings are designed to be inline with the center of the wheel, meaning that the loads will be primarily radial loads. When you move the wheel out, you will be creating an off centered load against the bearings. This can cause premature bearing wear. Having said that, most of us use 10 - 15 mm spacers. 15 mm is roughly 1/2 an inch, so I do not think that little of an offset would be much of a concern.