Here are three screen shots from a UCSF discussion about the risk of large cribriform.

As others have mentioned when you have a prostatectomy, they removed the prostate completely. The urethra goes through the prostate, what they do is sew it back together after the prostate is removed and put a catheter in to allow it to heal. It does reduce the length of the urethra since the part that went through the prostate has been removed. That can actually reduce the length of the penis.

You want the nerves spared if possible. Those nerves allow you to get an erection, Without them, it is much harder, and may only be possible using injections or an implant. Sometimes they can only spare some of the nerves, but that still can help you get an erection on your own.