Large heavy rugs are unlikely to slip, smaller lighter rugs on a shiny hardwood floor could spell disaster especially if you were carrying a tray of red wine glasses filled with a fine Bordeaux.
I don't have any first hand experience with this but I've read that in addition to preventing the rugs from slipping and sliding they prevent the rug's backing from wearing the finish off your hardwood floors. Also, pads with a smaller and tighter pattern are also supposed to be better for the same reason.
LMAO! I was thinking the same thing and came to my own conclusion that it was something to keep 'her' knees/elbows and forehead from getting rug burn; yes this occured to a girl I fooled with back in high-school. Didn't notice until people at school pointed it out right after lunch-playtime. pure comedy.