It's supposed to add room reverb. Similar to the air and ER settings on the pods for mic placement. The effect is more noticeable on headphones. Ramp up the mix and adjust the settings with phones on to hear it then dial the mix back. It is subtle. I have been leaving the reflections at 4 or 5 as a starting point. Like sitting in a standard room. Usually have the mix fairly low. Still getting my head around it as well.
I use it on my G3 when using headphones. Adds some nice space to the sound without resorting to a delay on one side of the stereo image. Real shame the POD HD doesn't have something similar, would make using 'phones so much better.
Of no use into a mono amp - but great for headphones.
Well I'm using the the G5 on stage so I guess it won't matter If I use it or not. I run into 1 channel of the PA from the "L" mono 1/4" jack. Now I know why I couldn't tell if it was on or off. Any setting make need to be for a live situation.