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If you wanted to take a picture with you subject off center, it's very helpful.
Like taking a pic of a person standing in the right 1/3rd of the shot, with the distant background taking up the remaining 2/3rds.
Without a way to "force" your camera to focus on what you want, it would simply default to focusing on the center of the shot, in this case being the background.
It also comes in VERY handy for "macro" shots. (very close-in subjects)