AC/AP allows Es' and SEs' to purchase a full fare Y or J ticket, and get a companion ticket with points. The reward ticket requires less points as a companion ticket than it would as a stand alone reward ticket, and it comes from J/C space as opposed to D space. This latter part is of huge benefit to an E.
I use the BATCAT for flying YVR-OGG, J fares are reasonable, and the companion ticket is only 50,000 points, and not subject to capacity controls.
The other nice feature, is that the two travellers, only have to travel one segment together, not the entire trip. Usually this is not a big deal for us, but it can be useful to be able to travel seperately.