I just caught up on this show and I agree that the meat looked really, really good this week.

I have used this salt baking method once before to cook a large roast, and it works really well. In my case, we did it on an open fire, so the salt casing helps protect the meat from the variable temperatures of the open fire as flames/coals ebb and flow through the hours it takes to bake. The salt really does harden into a shell as it bakes thanks to mixing in the moisture (egg whites). This traps in the moisture from the meat as it cooks, essentially steaming it. It takes a lot of salt to do this well, so I imagine you would only see this in the traditional food of maritime locales where salt would have been readily available. The salt is not reusable afterwards.

In a restaurant setting, I would imagine they could achieve much of the same effect through commercial steam ovens. This lets them bake a roast while injecting steam into the oven, keeping it just as moist (and cooking it faster without having to heat the meat through the shell). They might wrap it in something else that helps keep the juices in while also allowing better heat conduction.