Does underwear have a purpose other than looks? Is fresh air better?

Underwear. Provides an extra layer of protection in cooler climates & extra layer of coverage in societies concerned with modesty; also helps prevent urine/fecal stains of outerwear, which tends to be more expensive & more difficult to launder. Going "commando" is touted as "liberating" by some but may prove embarrassing in some situations. Too tight underwear can cause problems as well.