I’m pretty sure Frankie wasn’t talking about sirloins and saddles of lamb but the important word here is RELAX. Every chef I know worth their salt* and every time you watch someone cook on television they will all tell you to let cooked meat rest or relax. It is just not important it is imperative! An impeccably sourced, correctly seasoned piece of meat will be dry and tough if not allowed to rest.
It’s really simple, after cooking, keep a steak warm and covered with foil for 5 minutes before serving. For an average chicken or joint of meat cover with a foil tent and keep in a warm oven for 20 to 25 minutes, about the time it takes to boil the carrots and make the gravy. The core temperature will actually rise and the meat will reabsorb its natural juices making it tender and tasty. From a duck breast to a glazed ham to a whole side of beef, when allowed to relax the difference is truly amazing.