But the most useful function these hairs have - the sensory one that alerts us to the presence of bugs - didn't even get a mention!
Hairs extend our sense of touch beyond our skin into the air around us, detecting puffs of breeze and even the vibrations of the wings of passing insects, with no direct contact required.
Add some (supposedly vestigial and useless) goosebumps and that distance is extended to it's maximum, the hair shafts separated so any vibrations or displacement are less dampened by contact with the hair around them, aiding sensitivity. This happens during fright or arousal, when maximum sensory sensitivity is most useful.
Please don't let the myth of functionless body hair and pointless goosebumps go unbusted! --Ken F.