enemas and cleansing

i havent done enemas and am not that familiar with them. i think i could figure out how to do it, but my question is what exactly does ann enema do aside from a bowel movement. i mean i know people do them for constipation, but what i mean is that , what are the benefits? do coffee enemas help prevent colon and rectal cancer? what about herbal enemas, what do they do? and what kind of herbs are used? what exactly does an enema cleanse inside the body? i really for the most part do not believe in traditional medicine and i think it seems logical that a lot of disease is due to backup of toxins in the body although a doctor would never tell you this. anything i do to my body i want to gently and myself not have it administered. thanks for any opinions or advice.