One of the benefits is the availability of Radiation after RP should it become necessary. If you have radiation first, it's likely that the tissue will become damaged to some degree so should you have a recurrence the operation as a secondary treatment becomes somewhat more difficult and specialized.
That was the deciding factor for me...and I had a recurrence, simply went or the 39 radiation treatments and ADT. Doing okay for now.

Best of Luck to you!