Quoth the momma, "You never know when you might be in an accident and don't want anyone to see your dirty underwear."
Gruns, keep the treads off of the outer threads, thus requiring less laundry. Underwear as outerwear is less laundry, but then, why bother. I think that the problem is clothing period.
If my pants are tight and gritty, silky underwear could be an improvement, but I've got no experience as a woman.
Jbee