When cooking meats, it is important to remove them from the heat a little early. Flank steak should be allowed to “rest“ for 5 – 10 minutes, but a larger cut needs to rest for at least 15 minutes.
After removing meat from the oven or grill, the internal temperature of the meat continues to rise (some people call this carryover cooking). Without the continued high temperature of the oven, the external temperature of the meat decreases, however, and the result is redistribution of the juices in the meat, making it both easier to carve as well as more succulent.
If you are cooking with an instant thermometer, figure that the internal temperature in a smaller piece of meat will increase by about 15 degrees and a larger piece by about 10 degrees while it rests. For example, after cooking a pork tenderloin to 135°F in the oven the temperature will rise to 145 – 150°F as it rests.