It's part of the booking process. Once you've made your booking, the next page offers you standby upgrades. I ignore all of them unless it's to a room that gives me a water view (obviously, not Vienna) or additional space. I thought 27 euros for a junior suite (from the already upgraded premium room) was good value. You only find out on check in if they are able to give the upgrade. Radisson Blu Style had worked the standby list and had a junior suite blocked for us when we arrived.