those descriptions are not correct, they are overexagerating the effect unless they are refocusing on the other part. if you keep your technique good when you recompose the distance does not change THAT much
There's plenty of advice on how to select your focus points already, so I'll pass on info as to why Focus & Recompose Sucks...
Thank you, that really illustrates things!! This may be why I've had so many soft shots starting off with my camera....I was thinking I sucked, or that maybe my lenses and camera were faulty...but this may explain a LOT.
Applying some trigonometry, varying the angle, keeping distance to focus point the same, one gets the following:
Distance=8', angle=5 deg, the error is 0.3667"
Distance=8', angle=10 deg, the error is 1.481"
Distance=8', angle=15 deg, the error is 3.386"
So depending on DOF you may or may not notice too much of focus error...