In the london TMA, there is no planner and one coordinator takes and makes the phone calls for up to 4 or 5 "tactical controllers", So the need for a phone call to say "so and so is on a heading," would take up a lot of time. Asking the pilot to report it cuts this out. the same goes for speed restrictions. Sometimes you can even ask the pilot to giv e you his speed restriction if he forgets as traffic right up his chuff not working you yet tends to be a giveaway!!