In Perth, WA, the term "maintain runway track" was introduced to allow the departures controller to cancel and aircraft's SID on the ground and fly the runway track.
This was necessary as a number of the SIDs are designed to take aircraft around the Pearce restricted areas and have multiple VNAV and a number of heading changes. When the RAAF are not there we needed to be able to track shorten and let aircraft do what they needed to on departure.
ATC may not radar vector an aircraft below the MVA, if the aircraft cannot do its own terrain clearance e.g. by night or poor vis/low cloud. So a little creative thinking, all the radar SIDs are based on firstly maintain runway track (PH2 e.g.) using the obs clearance and tracks in the radar SIDs, we were able to introduce "cancel SID, maintain runway track.." for the 03 deps north and the 21 deps west.
Also this allows us to comply with noise abatement procedures and transition the aircraft from runway track to either direct tracking to the next waypoint or onto a heading.