When you bench test a shock with too much air in it it can have free/loose spots in its travelle. It should a have smooth consistant stroke/feel on comp and reb. On the bike a shock with too much air can soon land you in hospital. When the shock and the air gets hot the air will expand and the shock will feel like a pogo stick, very loose with no comp. or reb. control because as you can imagine air offers no damping as it passes thru the shock piston. The shock could also blow.