To instruct a pilot to fly a radar heading always brings the question to mind when I hear "Climb/descent to FLXXX and maintain". AS OPPOSED TO... I.E. There is no such thing as a radar heading. If you are under radar control all headings are radar derived. If you are under procedural control headings have no use, as no procedural separation standards utilize headings, but tracks.
Also, whenever an aircraft is taken of its flightplanned route by means of a heading, a reason for this must be provided. "to facilitate climb, turn left heading 180 degrees." Approach control will circumnavigate this in some cases as most STARs state to expect radar vectors for the LLZ.
Finally, how many out there provide the track required back to the next fix on the flightplan route if you took them of that original route?