OP, so you were also watching the JD and Jasmine Star's "The Art of Being a Second Shooter".
I find the back button focusing (BBF) a fantastic option when doing work with still subjects - landscape, flowers in a garden, still life, portraits of adults etc. That is where I have enough time to focus and recompose. And it is so handy for the focus and recompose style of shooting (especially when you camera has only 9 AF points) But recently I was photographing a couple of toddlers who keep on running around and found that shutter button focusing (SBF) suited me more for that purpose (but that may be due to my limited understanding of the technique till now).
When sometimes I hand over my camera to another person to take a photograph of mine (or a group of people including me) I find it very difficult to explain to them the BBF. So I just flip the switch and change it to SBF. At least for my 40D and 50D it is very easy to do and moreover I have saved the shutter button/back button operation menu in the MY MENU set up to be able to do it fast when faced with the need.