I remember when I spend a few days with a relative, who kept the (central HVAC) fan on all the time. I got used to it and didn't notice, until it stopped from a power outage.
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Most of what I've seen is vents in the ceiling. However, I have seen a few systems with vents in the floor (often in mobile homes).. I've never seen vents in the wall or both floor and ceiling.
I got new A/C in 2013. A good time, since we've had much greater humidity around June since then.