Got it when I got serious about off-camera flash. Makes setting up multiple flashes with varying ratios pretty straightforward, along with balancing the flash exposure with ambient. It's the meter I used to determine the amount of flash power to use to get the proper amount of fill in Keith's tread that I kinda hijacked. In my experience, I would set the power levels of each flash (assuming we are using multiple flashes) separately, and verify the contribution flash by flash. Then once all are set at the correct power settings, at the right distance from subject, etc., I'd take a final reading of all the flashes firing at once, to verify the exposure. After that, it's mainly adjusting the location of the flashes or the modifiers to get the amount of shadow, fill, and wrap-around that I'm looking for, and that last step has to be done using the camera. The ability to "integrate" several flash exposures is a neat idea, but I haven't had to use it.