Now, I agree with the general sentiment that it is an over done exam, and that the old "only two reasons not to do a rectal" line is mostly good for getting the lazy/scared MS3 to do the exam...
BUT
I still think they are useful! Even as a grown up attending, i still do my own rectal exams!
(1) Random old gomer with new/severe anemia: normal stool versus melena is a useful finding!
Yes, yes, I know you are going to admit them anyway, and one day they will have a BM that a nurse could check for you.... but finding that sticky, smelly unexpected melena is a true diagnostic joy which the skittish, squeamish, weak-willed among us will never taste!
(2) Prostatitis: It is real. Hard to diagnosis it otherwise. Man up and poke that prostate!
(3) Peri-anal, peri-rectal, peri-peri abscesses: useful to do a rectal. Or just chicken out and call the surgeon. Your choice. (*bock bock bock* *flaps wings*)
(4) Neuro examination: I would argue it is rare to have low tone be the ONLY finding, but when there are other findings of potential cord injury or cauda equina it is useful. I certainly don't do a rectal on every back pain patient. But maybe I should. No oxycodone without a rectal. We could put signs up!
Now, does every body with a couple blood streaks in their BM HAVE TO HAVE a rectal? Of course not. But I wouldn't fault you for doing one. Same thing for someone with pain during defecation.