I've had one for a few years now, in both multi FX and my Digitech BSW (which does a great job in this role, incidentally). In the past, I've always used it whilst playing in the mid-to-upper range of the instrument (say, C on the A string and above) with a good proportion of the wet signal mixed in. But just recently, I've taken a liking to playing down pretty low - say, bottom G - with just a tiny, barely noticeable amount of the really, really low frequency wet signal added. You can't really hear the sub-octave distinctly, but somehow you can feel it and the sound gets pretty beefed up in an almost subliminal way. It's a fantastically cool effect, I think, and hopefully the very low amplitude of the very low frequencies - down to 24 Hz for the G - won't wreck my drivers too quickly (I hope). It's only a tone below the bottom note on a piano, after all. EDIT - I do understand that there won't be a lot of the lowest fundamental in the signal, but I'm still cautious because doing this obviously increases the LF content of what gets to my cabs.