As the acoustic guitarist in a (mostly) electric band I do this a lot. As Willie-O mentioned earlier you can get the tonal effect of a mandolin -- and I know a lot more chords on the guitar than I do on the mandolin. It's good to do in sessions as well, for the variety, and it keeps you on your toes too, doing instant transpositions in your head. Makes you think that maybe you COULD cut it with those Nashville guys and their numbering system (if only!)