The replies above have addressed. Consider some other points: you can 'focus and recompose' with BBF. I do this sometimes when I want the 'focus' to be someplace just outside the limited-size AF array of my older cameras. I use the nearest AF point and focus on the subject with the BBF active. I then release the button and adjust the composition / re-frame to what is desired. Then, just release the shutter.

Other times, I'm shooting with a cable release and tripod. I set-up the camera / tripod / composition and press the BBF for the desired focus. I then remove my hands completely from the camera and stand back and release the shutter via the cable release.

As long has you have properly reprogrammed your camera buttons, the shutter button will no longer activate the auto-focus. That is, you program a button on the rear of the body to activate the AF and you re-program the shutter release to handle only exposure and shutter release, removing the AF activation.