I had to have one a few years back whilst I was being checked for colon cancer and, all I would say is - Don't knock it till you have tried it !
It is not something I was looking forward to but i have to say that i felt great afterwards and for a few days I just felt better - hard to put a phrase that catches it but i was more energetic, felt cleaner and less stuffed up.
I am not sure if it was something I would pay to get done regularly but there is definitely a positive side to it