The theory is that a higher concentration of bile would expedite lipase activity. This is because bile emulsifies fat, creating greater surface area over which the lipase can react. A higher concentration would emulsify fat faster, thus allowing the lipase to work more quickly.
It follows then that a concentration that's too low would allow fat to linger undigested for a longer time, which causes a host of GI disorders including cramping, diarrhea, etc. These are symptoms of patients whose gall bladder (the bile storing organ nested in/near the liver) has been removed. They generally avoid fattier foods as diarrhea and discomfort can result.
Too a high a concentration would result in an excess of the components of bile; cholesterol, bilirubin, phospholipids and bile salts. Each of these carries their own dangers in high concentrations that you should be able to research easily.
I hope this helps.