On the E Jets the radios are primarily tuned via the MCDU. Usually the numeric keys are used to input the frequency in a very convenient and direct manner, but it would also be possible to tune the radios in a more traditional way via the rotary knob.
Additionally the OAT and Assumed Temperature for the desired take off thrust setting must be entered/dialed in using the rotary knob. I always guessed this was a feature to avoid blunt mis-settings, as it would rule out finger troubles.