[Arran]

Potting keeps the elements out so the wires don't oxidize as readily. Plus some immobilizing which helps.

Mike;
  The reason that I was told as to why RCA had these potted was supposedly to discourage rivals from reverse engineering their superheterodyne models. I don't know if this entirely makes sense as RCA, as a patent pool, had a virtual monopoly on the superheterodyne circuit which only allowed G.E and Westinghouse to manufacture them, and under which they issued threats of litigation with great zeal. Whether it was potted or not, patent protected or not, it still did not prevent other companies from infringing on their patents, particularly the makers of kit radios. In any event I have a Canadian Westinghouse model 89, which I think is similar to an RCA Radiola 62 or 63, and none of the RF or IF coils are potted, only the condensers, chokes, and the power transformer, so they obviously thought that it was unnecessary by 1927-28.
Regards
Arran