skim dry for daily 'normal' conditions, the skimmate is concentrated and kinda thick. Wet is well.. wet. tint of greenish brown water.
you can set the skimmer to run wet or dry depending on food/bio load. I generally keep mine pretty dry until it's time to dump the container, then crank it up for an hour or two to clear the goo out of the hose leading to my gallon jug.