I know of at least three reasons for a DRE post RP:
1> Fistula. When a prostate is removed the body changes. If you have ever had post RP radiation you know this. Typically the bladder sets into where the prostate used to be. We are told to drink lots of water to pull the bladder back out of that area. But also it is possible for a rectum to ease into that area and it can cause fistula. This can be an issue later in life and a DRE can detect it. But many doctors won't do it unless there's a complaint.
2> Growths ~ either benign or malignant. It is possible to feel recurring PCa, but it's also possible to feel other growths.
3> DRE's are not just for prostates.
www.webmd.com/colorectal-cancer/digital-rectal-examination-dreI thought for a fourth reason ~ a secret handshake between doctors, but I have since eliminated that as a reason.
Tony