You'd be surprised at how much 10mm can upset the factory geometry and loading of the hub and more notably the bearings, particularly the way the are loaded radially.
With suspension, even the smallest of changes can be exaggerated elsewhere - camber is only measured in single degrees, which again seems a trivial measurement on a small scale, but can make an enormous difference by the time it's multiplied through the height of the wheel.
Elementary physics says that as you move the load away from the fulcrum, the force increases - a lever. By using a spacer you are basically changing the offset of the wheel, multiplying the forces on the hub by moving the wheel further away from it. The result is increased loading on the bearing and accelerated wear and ultimately - failure.
Obviously, the size of the spacer can make a difference but don't under estimate the difference 10mm can make. Also, when making a modification like this that is easy to do your self, be sure to get an alignment check afterwards.