Say you would like your steak grilled rare. If you grilled the meat on high temperature, you’ll need about five minutes of resting off the heat to allow the temperature to transmit from the crust to the core of the meat. Otherwise, the meat might still be cold inside.
The advantage of allowing meat to rest after cooking is that fewer juices run from the meat when you cut it. Another function is to let the heat penetrate from the outside to the core during resting, which is called “carryover.” The drawback of resting is that (and this goes for all preparations) the crust becomes softer, due to moisture exuded from the meat. This effect doubles when resting meat using foil or parchment paper—and it’s a shame, as you’ve just put so much effort into creating a nice, tasty crust.