So I read somewhere that the mesh size won't effect the amount of force transfer occurring between bodies if several bodies are in contact, and a global force is applied somewhere. I wanted to know why is this the case?
Forces do not disappear without resistance. For a statically balanced system, globally, the sum of the applied Forces must equal to the sum of the resistance forces, so the number, and size of the mesh will not affect the result.
However, the number and size of the mesh will affect the pattern of the internal forces/stresses. Usually, it is advisable to provide finer mesh near the concentrated forces, sharp corners, and openings where distorted results may occur due to stress concentrations.