I have had some good experiences, and some that didn't matter. At the DoubleTree Amsterdam, I knew the odds of an upgrade were slim, but I used the app to choose a room and got an awesome room that was pretty large, looking over the city, and high up, it was exactly what I wanted. That was a revenue ticket. Another time, at the Hilton Orly (points + miles) I chose my room but got an upgrade at the front desk to a nicer room (relatively speaking). One time in Rancho Mirage, the lady at the desk said that the room I chose was noisy, and suggested a room looking over a quiet courtyard, so I took her advice. So, try it, what's the worst that could happen?