#1 It relaxes the biliary ducts helping the bile to move freely through the liver & gallbladder.
#2. It relaxes the musculature of the colon, assisting one to retain the enema for the optimum 12-15 minutes. (Some people really need this, others don't at all).
I become very dehydrated when I use ES and so I have started using only a teaspoon (or none at all) for a 1 quart enema. But my husband uses two tablespoons and has never had any difficulties or problems.