JR1 wrote:
Never used it and never will, half press the shutter release when focussing
Back button focusing is very useful when recomposing and when shooting with a full time manual focus lens. Using it or not really depends upon what you are trying to accomplish. Its ability to separate the metering function from the auto focus function gives the photographer greater control over the results. Most, but certainly not all advanced amateurs and professionals tend to use it at least part of the time.