I am hobby photographer and started only couple of years back. For the first year of my photography life I used the "normal" shutter-button-do-both everything process. Meanwhile I learnt the focus and recompose technique - and I was so horrible at it with the "normal" use of shutter button. Sometimes I would press a little too much and take a photograph a frame that I never intended to, sometimes I would forget to keep the "half-press" on and after recompose when press the shutter button the focus will be automatically redone. Ok, I admit I might be at fault here for not being diligent and able to master the "half-press" thing even after a year. But then I read somewhere about the back button focusing and changed my canon 40D's setting to do that. And man it was just like "eureka".... why is not this the "normal" process? what is a "half-press" really? Anyway, I now use back button focusing for all the reasons and benefits that the other CRians have written above. and I am happy. The only flip side is if I have to give my camera to someone for taking a one of photo of me in a group photo. I have to explain to him/her how to "differently" operate my camera than he/she normally does his/her point and shoot.