Air deflectors on floor registers and cooling efficiency
The past home owner left these in my place.  Where the blowing air just gets caught behind the curtains, is under furniture or tropical plants, I divert it, and this just happens to be towards places where people sit.

Keep in mind in the winter, having the warm air low helps mix it.  But in all seasons, the vents are near windows and doors to counteract the cold/hot spots these create to give you a more even temperature in the home.

Also, if you have moisture problems in your windows, it's not because of these deflectors.  Well insulated windows (multiple panes and weather stripping) are the solution to that problem.