This is commonly given to those who have succumbed prostate surgery, and to persons who are believed to have a psychological blockage when it comes to getting a full erection or keeping a persisting erection throughout intercourse, this is common in those who have had various conditions of depression or anxiety.
I fell into the latter group myself, but the psychological blockage was quite complex, many years of depression, I had also been jerking off daily for 25 years, watching adult movies daily. Firstly I did develop death grip after years of anti depression medication, and secondly after watching adult movies for literally 25 years on a daily basis it was becoming impossible to fuel my erection without adult movies.