Trees should be trimmed for a specific reason. They should be trimmed so that continued growth will not interfere with houses, power lines, or other trees. If you have a tree that is too large for the location, the only real option that you have is to remove it and plant a tree that matches the area. The materials mentioned above lock in moisture, accelerating the decay process by providing the perfect habitat for wood destroying fungi. Dark, warm and moist.
Paints do very little to keep out insects and disease.
Trees naturally harden-off, by forming a protective barrier, within 48 hours. Here's an analogy. Of course not, but this is what happens when a tree wound is painted. When a limb is cut or torn, cells are severed, releasing all kinds of good stuff in a wet solution. Pruning paints are used where Oak wilt is found, and to control the peach tree borer.