There will always be shadows. There won't always be rain.
Therefore shadows > rain.
exactly.
rain under a roof is pretty rare in skyrim, i assume. most indoors, as said before, will be seperate cells behind loading screens.
shadows, however, contribute a lot to the fidelaty of the scene and exist everywhere.
if there WAS a connection between rain and shadow i'd take shadows over rain. but i dont see any relations.
we will have to endure the rare occasion where rain (and probably snow) will fall through solid objects.