If you're working on an image in Photoshop that's cut into numerous sections, sometimes you find yourself needing to carefully align the different layers just by eye. Set one layer to the "difference" blend mode, though and it's infinitely easier.
This video from Scott Kelby shows how it's done.
Usually when you're trying to align layers that overlap, you might set the opacity down so that you can see through the top layer to get them aligned. Even then, you might end up a few pixels off. As Scott demonstrates, setting the blend mode of the top layer to "Difference" makes it much more obvious when image is perfectly aligned. Watch the video and you'll instantly see why.
It's a fix for a very specific image-editing situation that I frequently deal with, and this is so simple and obvious I can't believe I haven't done this before.
How To Perfectly Line Up Anything in Photoshop Using a Blend Mode! [Scott Kelby via PetaPixel]