In Europe, where many properties charge extra for extra people, it is important not to mess with this stuff. In places where "rules are rules" it is easy to find yourself paying the rack rate or being required to take an extra room.
On the other hand, when you call ahead and deal with these things up front, you would be surprised at how quickly extra fees & charges can drop off your bill. Or maybe the rollaway gets charged, but a nice dinner is comped.
All about how you deal with people.