Ummm, maybe so if you dont give a dept report within 10 min they know which end of the runway to send emergency services to look for you ?
I always call ctr with my callsign only on first contact, sometimes theyll come straight back with my clearance and code, sometimes they tell me to stdby. Ive been told off for making my first call an all in one (vfr into CTA), I guess it depends on the controller and his workload/mood at the time.