I'm a holdout. Most speed scratch cooking methods leave too much to be desired. There is no way to mimic the outcome for roast that has been cooked slowly, for hours at lower temperatures. The flavors are marvelous. But, I have a burning question: When a chef, or your Mom, tells you that searing the roast "seals the juices in", is that based mainly on historical belief, or is the cook always right?
It's one of those repeated pieces of information that sounds like it has myth potential. For example, today I started cooking a rump roast. This is a thick piece of meat, from any dimension measured. Searing the surfaces would do two things that would account for improved flavor: 1) It would produce some Maillard browning, and the flavors that result from this. 2) It could also deter the active growth of bacteria, which will probably be in higher numbers on the surfaces. When you put a thick piece of roast into a container and cook it slowly, the slow change in temperature gradient could allow several generations of bacterial growth to progress. It may also have some effect on enzymatic change. But how can the process of searing effectively "seal in the juices"? And if it does that to some extent, does that really matter in the overall flavor development?