AC Ops can also control traffic in certain situation. Tac Hel squadrons for example will have one ACO and a team of AC Ops, usually comprised of a Sgt and a number of MCpls and Cpls. The AC Ops can provide advisory support to aircraft in the helidrome's immediate area as well as link with civilian ATC services where the aircraft are filed IFR out of the helidrome's controlled airspace, into controlled civil airspace and up onto IF airways. Often, the ACO may actually be involved in Squadron operations, and leave the majority of the controlling and advisory to the NCO I/C (Sgt) and their NCMs.
At larger bases, one often sees the AC Ops specialize into the provision of IFR services including precision radar controllers. ACOs will control the tower (VFR and IFRs arrivals) and the terminal area (positioning aircraft for landing and instrument approaches).
That's from the inside cockpit point of view and having had an ACO work for me as a deputy operations officer. ACOs and AC Ops can tell you about what a PITA it is putting up with aircrew on the other end of the radio... ;D
Regards
G2G