The priority lane is a joke and doesn't work because of the way GTAA manages it:

If it's busy, most of the travellers coming through are eligible for the priority lane, so the priority lane is the busiest or just as busy as the other lanes. This does not help you get through security faster.

If it's dead, CATSA opens the priority lane to everyone, so you also do not get through any faster, because they try to equalize the lines to maximize the number of people getting through the security lines.

What they should do is allow non-priority passengers in the priority lane when it is dead, but allow priority passengers to go ahead of these passengers by having a split lane before heading through the security door ("real" priority and "overflow"), so that priority passengers get through faster even when it's not busy. Then this would be a useful perk.