Sure grip or not, the center spacer performs the same function. It floats back and forth depending on axle shaft loads. Pushing the RH axle in all the way also pushes the LH axle shaft out against it's bearing race and vice versa. Too much end play can cause oil to "pump" out through the axle seal and in severe cases, noise, brake problems, and odd bearing wear. Too little clearence can overheat the bearing and cause it to fail.....sometimes by locking up and spinning in the housing and/or on the axle shaft.
