I saw a college experiment where different fan locations and directions could actually make "null" areas that caused overheating. And with modern hard drives, RAM, VRAm, etc. all preferring a cooler environment things could become very bad very quickly if the fan configuration was wrong.
Plus more air movement can equal more intake of airborne fluff and dust that could get trapped and thus cause overheating.
Most of the electronic equipment I used in the RAF had air filters, but I've never seen filters on PC's.
