Lol, have you seen the immigration queues before this system was implemented? If you have the cross over your name, then you have to go to the regular queue, otherwise, there is a faster queue to show the officer. Using APC means you are photographed and finger printed by the time you reach the officer. For my recent trip, there is almost no wait to first use the APC, then a shorter wait for the officer. With APC, the officer will not have to take your photo and fingerprint you again, or maybe for random checks, which greatly expedite the officer check time. They might have lesser officers on duty, but this was one of the fastest time I've seen to clear immigration, with me clearing before my luggage was even out. Previously, my non-priority tag luggage is out there already after I clear immigration. Or at least this way, they can deploy more officers to the non APC queues, such that in general, everyone waits a shorter period. Maybe next time, if you travel in a group, you should go to the normal queue while your friends go to the standard non-APC queue, see how much faster it gets.
Note that with APC, non-US residents with proper credentials get to go to the APC lane instead of being lumped together with the non US residents lane.
It is with such attitude that I see cars in SG carparks, where there are 2 exit gantries. Cars just refuse to go to the second gantry even though it is empty. Assuming 1st car goes to gantry 1, then 2nd car goes to gantry 2. 2nd car will still exit between 1st and 3rd car, but 3rd car will be able to reach gantry after 1st car clears instead of waiting for 2nd car to clear in order (instead of almost concurrently). Thus in general, the whole queue gets cleared faster. But drivers see no benefit in going to 2nd gantry, ie no queue cutting, so do not go there.