The no bone on bone thing does seem a bit weak with your metaphor
Sometimes that is the problem with metaphor... :-)
The issue is neither
Bone on Bone nor
Muscle on Muscle. What you are looking for is HARD on SOFT. Examples:
Elbow into the big muscles of the upper leg when seated.
Tricep resting on the knee when kneeling
Cheek (soft) on the comb (hard)
Buttstock (hard) against chest/shoulder muscle (soft, not the the hard ball of the shoulder joint or on the collar bone)
forend of rifle on a soft bag.
Bipod's
rubber feet on hard ground surface.
The REASON is to absorb movement and vibration. M25 is correct that the "rubberiness" of soft on soft doesn't provide stability, but the unsecured Hard on Hard (elbow on a knee, for example) passes every small movement (breathing, etc) through the entire system. It also makes it much harder to maintain the position or extended periods of time and almost impossible to maintain the position through recoil and bolt manipulation.
-RJP