Hello Phil, this is the type of question I love as it involves a bit of science, more precisely chemistry and thermophysics. Now that I so cleverly scared you all into not reading my answer (another illustration of my excellent PR skills), here-it- is-quickly-before-you zap-to-your-next-email: Cutting cooked meat at too high a temperature will make it lose its juices, yielding a less flavourful and drier piece - no matter how much love and good karma you put into its cooking. At lower temperatures, the meat has a higher ability to retain its juices when cut. This is why you want to let it cool down a bit before carving it. Now the full explanation (I couldn't hep!). At high temperatures, the meat's tightly woven strands of proteins become fragile and breakable and the collagen proteins, which are responsible for keeping the meat firm, liquidize (this is the reason why cooking meat makes it more tender). As side effect of this transformation is that the proteins lose their juice holding properties, so if you cut your beautiful roast at too high a temperature, most of its juices will run out. If you wait until the temperature drops on the other hand, the protein web will strengthen again and regain its juice holding properties, keeping all the flavour and moisture when cut. How long to rest? The resting time should be long enough to allow the temperature to drop all the way through the centre of the meat, which keeps cooking for a while after being removed from the heat. Some chefs suggest 8 minutes per pound, in practice you'll want to wait 7-8 minutes for something small like a steak and 20 + minutes for a bigger piece of meat such as a roast, keeping it under a loose aluminum tent to prevent the sides from cooling down too much. If you are a hard core number guy, stick your probe thermometer at the centre of the meat and let it cool to 50 degrees C (120°F) at its centre. Then you will have reached the optimal carving point!