i would have to say that clearing a wash will provide you with a more stable boil. Think of boiling piece wihch are placed inside your pot. if you have a ton of slugde kicking arounf the bottom it will not boil as effectivly. Also I would assume that the column (when doing large runs) may begin to lose effective plates since the packing will begin to get dirty. but i am not a chemist, I am only thinking out loud here..but I do know that the cleaner the wash the easier the clean up afterwards...