Just that really.
When I lost my sense of smell and taste with covid it was really strange. I could breather perfectly well, but even with my face shoved in something stinky, I wouldn't have had a clue.
When people say they have lost their sense of smell with a cold, do they mean it just disappeared, like with covid, or do they mean they were so bunged up they couldn't smell anything? It must have been pretty rare before, surely?