Basically, it provides bulk, which in my case eliminated the cramping and diarrhea, and therefore the unnecessary stress on the colon. Fiber is also essential to keep things moving through the colon in a healthy way.
The article hot linked suggests we skip the supplements and focus on high fiber foods. While I generally agree with that sentiment, it is very difficult to get in all the fiber we should have to promote good gut health, therefore the supplement.
One of my questions to my doc, was, "Can I safely take this every day?" His answer was yes, yes, and yes. I asked him if he took the supplements and he told me that he does, never misses a day....he had the same surgery as I did.