I use this trick too for puzzles! Spotting on the fly the differences, makes for a great intro of the topic with people not aware of it!
It's amazing that this shows our visual system constantly doing a type of low level computation to calculate our stereoscopic 3D vision, and that we can "exploit" this hidden computational power to easily image find differences.
I remember reading that this was actually how Pluto was discovered: Someone compared a lot of photographic plates with this method.
For Pluto, for what I know, they did use the technique of taking two images of the sky at different times and looked at them through a machine, but instead of relying on stereoscopic vision, they switched back and forth between the two, everything that isn't the regular star background would be moving or blinking.
So, relying on movement perception.
So for example today I was cleaning up a server, freeing up some space, and then made it send me a storage space summary. I compared that one with the one I always get sent at midnight, put them side by side, and compared them via the cross-eye method. Small differences are always noticeable.
I also consider it as my cheat in order to solve those puzzles where you have to find the differences between two images, it doesn't get any easier than this.