I've used it to get out of the way of a lot of other notes in the lower register of the guitar, like the left hand of the piano, other guitars, banjo, various mandolin related instruments, etc. Others have used it to get something approaching that chimey 12 string sound without the additional strings; to mimic (not so well) other instruments like mandolins, or just to get other chord "voicings". In groups with multiple guitars, a high strung one can be a nice alternative.

Peace, Mooh.