They are very welcome, like baby smell or popcorn. Or, they can be unwanted. Like any kind of fish. Urgh, gag me.
Smells are also the things that can transport us back in time.
I walked into the BF's house today, and I was back in the next door neighbours house, with a million (ok, exaggeration) cats which had peed all over the house.
So not into stale cat urine. And it was inside the couch, so I smell of it now and will need to launder my clothes.