1. When meat is pulled away from the heat source (ex. stove top, oven, grill etc.) it is still cooking. This is called carry over cooking. Once pulled away sit the meat to the side and cover with aluminum foil to keep warm. This is why most recipes call for the cook to pull the meat away from the heat source a few minutes before it is done to prevent over cooking.
2. When meat cooks the fibers in the meat firm up pushing all of the moisture out. So when the meat is in the resting period most of the juices will redistribute throughout the meat.
(When you do cut into your meat right after cooking....you will notice all of the juices running out)
Resting time solely depends on how big the meat is. It can range from 10 minutes up to 30 minutes.
However; today I must say. I didn't let my meat rest. It was so mouthwatering that I had to cut a corner out of it (top left corner missing). I just couldn't help myself.... I am sure that I'm not the only one that have done this that clearly knows better.