someone posted that the use of expedite when critical separation is not needed - ie the a/c are on headings that will maintain separation. Surely in a busy environment like the TMA if an aircraf tis put on a heading it might well be off the normal routing - and in temrs of an inbound descending through an outbound (and vice versa), the conflict is resolved quicker the aircraf tput back on own nav quicker and the inbound transferred to approach quicker etc.. thus freeing more time for the next conflict to be resolved. Also it might just mean that a direct routing becomes available as conflicting traffic is out of the way