Hm, that's not my experience: I used all three options (no hood [student dorm], circulation hood [currently in our house], outside duct hood [parents; last flat]). There is a huge difference between each. Having no hood is obviously not nice, since water vapor and fat end up everywhere. The circulation hood at least reduces the amount of fat. Not sure if by 20 or 80%, but there is a significant difference between turning it on or not. Especially the amount of fatty haze when making hamburgers is reduced a lot. Now for water vapor it does not help so well. It's okay for one pot of water (boiled eggs or pasta with pesto), but when doing some heavy cooking still a lot of water ends up condensing on the windows. With an outside duct (about 2m of duct work) water vapor becomes a non-issue and the amount of fat haze is reduced much better than with the circulation unit.

Also this isn't biased by "I don't cook". Quite the contrary :)