The main goal of the thong style is to provide coverage and protection between your body and your clothing, without showing through. Many women prefer the style with form fitting pants, skirts and dresses and also feel the style gives them added confidence for intimate occasions.
Thong panties are similar to seamless panties, which helps in keeping those panty lines showing through your pants at bay. The string at the back of the thong goes through the back to avoid any trace of a panty while keeping you covered and comfortable.
Comfort. While it's common to associate thongs with discomfort, it's also true that many under-wearers love to wear thongs for comfort! Some women find underwear with a back tend to ride up, move around, or basically turn into a thong anyhow while they walk or move around during their daily activities.