I was told once that the secret to great BBQ and roasts is to put your rub on it, freeze it, and then thaw it back out before finally cooking it. This sounds weird to me, but I thought it couldn't hurt to ask. Is there any advantage to this technique?
I am not so sure that it is a secret to next-level BBQ. Several BBQ discussion boards, as well as Reddit, have explored this topic. It seems that it is mostly done as a matter of convenience. For example, when purchasing a large quantity of meat (like at Costco or other bulk store). Many will season everything, and freeze what they are not using, to be thawed and smoked or grilled at a later time. I did not see any reports of culinary advantage, other than convenience. Though some even have smoked from frozen, which, of course, extends the cooking time. I guess the disadvantage would be if you decided you wanted to use the cut for a different purpose. You are stuck with the pre-seasoning. While this was not discussed, I might be worried that a seasoning with salt in it might create more of a cured texture on the exterior. That might be desirable or not. Finally, irrespective of seasoning, freezing and thawing does have the potential to impact texture. Particularly if it is done more than once. Again, maybe good, maybe bad, depending on preference.
It may be that the advice to freeze is meant to help with browning the outside while not overcooking the interior. See here for an experiment on freezing steaks. If this is the case, my recommendation would be to not thaw completely before you start cooking.
Another possibility is that it’s an attempt to tenderize the meat.
Freezing creates ice crystals that damage the meat fibers. Although this might be a problem for preparations in which the moisture that had been trapped inside the cells leaks out of the meat and leaves it dry, I suspect that in the right cut of meat at low temperature, it could help with the collagen’s conversion to gelatin (as that requires moisture)
I don’t have a smoker, or I’d try doing a side-by-side comparison— one butt that had been frozen, and one butt that hadn’t. I’d probably not try the rubbing, freezing, thawing, as it would slow down the absorption of the salt and sugar from the rub, introducing another variable.