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. 