If you're shooting one-off photos (especially in One-shot/single-AF modes), Back-button Focusing doesn't make sense to a lot of people I'm sure.
By my experience though, you shutter-focusers are all weirdos

Separating the focus from the shutter is almost a necessity for me when using AI Servo/Continuous AF (and really even one-shot) because I may disengage focusing at any time and essentially lock the AF to whatever distance it is, without compromising my ability to take my finger off the shutter if I need to.
Think about a scenario:
You're standing at the back of a church, shooting a 70-200 lens on a camera with a vertical grip. A bride is walking down the aisle toward the altar, and you're tracking her as she's walking away from you. She suddenly stops to hug a relative on the side of the aisle but the composition doesn't work for the way you're holding the camera, so you switch to the other orientation. You take your finger off the shutter and need to quickly shoot again. Do you have time to re-confirm focus before you shoot again? What if you were tracking with the centre AF point and want to shoot an off-centre composition? No time to focus and recompose - by the time you move the camera and lock focus again (needlessly), the moment is over and she's on her way to the altar without a photo of her and her favourite Aunt Milda.
Back-button focus would let you switch orientation and composition without messing up your focus and then once the bride continues up the aisle you're back to tracking her movement with a push of a button.
Apply this to your macro/wildlife/street/etc. shooting situations as necessary.
Back-button for life! (except when I hand my camera to someone else)
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