A SE can get instant KK (capacity control) override - ie if any seats are still available for revenue tickets, and the plane is not oversold, a SE can get those seats (even if all Aeroplan award seats on that particular flight are all "sold" out). This ability is there, whether a SE goes to a telephone agent, or books on-line.

In terms of a SE booking on-line, one has to book the SE button, to get the extra KK (override seats) - or even as a SE, one will only have access to the regular Aeroplan supply of award seats.

In terms of my own experiences booking on-line, vs with the telephone agent, I find that a certain percentatge of KK override seats which can be claimed through the telephone agent, are not available on-line.