The ASA dial on a Rolleiflex (without a meter. I don't know about metered Rollei's) is a reminder only. It has no effect on the operation of the camera.
With a coupled meter it changes the "coupling" of aperture and shutter time.
It also has a correction for filter use (at least in the 2.8F, don't know about other models).
I have a T and 3.5f. The meter on the T is really funky. The 3.5f makes seance. So on the 3.5f doesn't have correct Asa with film inside, it theorically possible to screw up a roll when developing.
ToddB
on my 2.8 E the asa setting wheel tells the light meter what speed of film the camera has in it so when I use the meter it tells me the correct setting for the camera. The meter isn't mechanically linked to the camera, I take the EV number off the meter and set it on the camera.
The needle on the meter isn't changed by changing the asa, but changing the asa shifts the little rings on the meter that tell you what EV to use when you match the needle up with the pointer.