Talking with some oncos who deal with high risk cases, they do use 3 year HT in some cases as they see a benefit in outcomes. The situations which tend to point to using 3 years are high risk cases (obviously), PSA not going extremely low after RT, and fit men who are unlikely to suffer significant comorbidities arising from the hormone therapy itself.
I haven't talked to my own onco about his criteria, but this might well be what he did with me. At the outset, he said I would be 18-36 months. When I was coming up to 18 months, he said I could stop at 18 months if I wanted to, because my PSA was <0.01. If my PSA had been still 0.5 or higher, he would have wanted me to do the full 36 months. I elected to go on to 22 months, as the HT wasn't causing me any issues which I couldn't put up with for a bit longer.
Time limited hormone therapy is always a balance between improving cancer outcomes, versus QoL reduction and risk of comorbidities arising from the hormone therapy itself (things like metabolic disease, heart attack, stroke, osteoporosis/fractures, impact on sexual function, etc). I think the key thing here is shared decision making - letting the patient know how much their chance of a cure increases, versus their chance of heart attack, stroke, etc which is calculable based on BMI, blood pressure, cholesterol, blood glucose, etc, and their own perception of QoL on HT. It is a personal decision.