'activating' the approach simply slows the aircraft down for flap extension,you can see where the 'managed'profile would do it on a 'decelerated 'approach.(a conflict in Canada as one has to be at 200k prior to descent below 3000agl,within 10nm of the field)
'Arming' the approach,when one is'cleared ' for the approach,or as the aircraft is turning in on'nav'(loc' alive)