I do believe that it does something. On the japanese car, the fans don't actually increase, all that happens is that air gets sucked in from inside the car instead of from outside of the car and you can hear the air getting sucked in. It's not exactly quiet.

On the mercedes the recirculate mode does work (at least in my car it does), but I would imagine that it's quiet because they designed it that way in an effort to make a luxury car.

The recirculate mode is only intended to be used for short periods of time. When you get in the car and it's very hot in the car then you might use the recirculate to try and cool the inside air of the car quickly for example. After that the A/C system would be working to try and cool already fairly cold air. This is no good. It's better for the A/C system to use the normal air mode as opposed to the recircuate.

It's also better not to use the recirculating mode when heating the car in the winter either, but for different reasons.