I have had many occasions at different airports flying a small single engine piston aircraft out of a Charlie or Delta and they will assign the SID, but give different instructions upon getting airborne. Is the SID assigned as a lost comms safety net? Or is there another reason why they assign the SID and then don’t actually have you fly it?
For example, flying out of KCHA, being assigned the Chattanooga Eight, and then being given completely different heading and altitude instructions open contacting departure. Same thing has happened at KAVL on the Asheville Seven.