Harder than you think. They have to be in the 100% right place, close doesn't cut it (unless they have changed since December). And it's not just a blue or green light that comes on when it's aligned......the light goes in circles and takes a few seconds before you (and the CM) realize if it's green or blue. Although the light spinning around the big Mickey icon is cute, it would have been faster if a light on top or something similar lit up immediately.
You wouldn't think a few extra seconds per guest would make much of a difference but factoring in 3 seconds (just guessing here) per guest at entry turnstiles, and twice through fastpass+ lines does add up over the course of a day and result in taking longer to accomplish the goal of entry (turnstiles & rides).