Wheel bearing spacers have been used in racing for decades.
Modern sealed hubs have the advantage of having nearly zero bearing movemet yet still be very little resistance, however they are expensive and are not servicable, sealed bearing hubs are not designed to handle the type of negative offset loads prevelant on older vehicles.
Introduceing the wheel bearing spacer, this allows both inner and outer bearings to suport each other greatly reducing the bending force on the pin and allows ful torquing of the spindle nut without locking up the bearings.
Cooler running bearings.
Near zero rolling resistance.
Reduced piston knock back.
Much reduced cost of operation. 
Sold in pairs.