The bolts themselves don't take the entirety of the shear forces. They provide tension and therefore friction between the mounting surfaces which is where the s

The bolts themselves don't take the entirety of the shear forces. They provide tension and therefore friction between the mounting surfaces which is where the shear is handled. By being loose, there is no friction to handle shear and also the item can gain additional momentum (more distance to travel) during shakes and impacts which might increase the impact force above the rated strengths strength.