One of the risks of surgery is that there is cutting in an area in which there are various nerves that control sexual function in males. 2% of males having surgery end up with permanent impotence and 10% with temporary impotence, based on what my surgeon told me. If you are single or want to have children in the future, you will be advised to bank your sperm. It will be prudent to do so, in the unlikely event that you fall into these very low percentages of persons rendered impotent by the surgery.
The surgery had no impact whatsoever on my own sexual functionality. I think my sexual functionality may have actually improved after J Pouch surgery, because I was not really sick any more.