The best I ever saw was a old Daiwa saltwater spinner I was working on.. It was their largest model so the cavity inside was very large. The entire thing was packed to the brim with black grease! It was unreal.. One of the worst things to have to clean up after. There was an unbelievable difference when it was cleaned out and greased properly.
I usually put a light coat on the side plates with a small brush. I actually think that if there was sand inside the reel, I would rather have it stick to the grease than to get into the other parts.. But it shouldn't be there to start with.