Definately a useful too for drums with multiple mics. I just recently had a "duh" moment realizing that the kick sounds way tighter and jives with the OHs much better if the wav's inverted. Same, or course, if you are micing the bottom of the snare. Otherwise, I can't see it being much use - maybe if you are micing the back of a guitar cab, which I've never tried. Maybe I will for the next guitar track I work on - just for fun.