Like many functions on dSLR's, they're aimed at people who like gizmos on equipment rather than photography.
If you're using an f1.4 lens, then you're unlikely to put the point of focus right in the very corner very often. If you do, it's unlikely to be terribly sharp because f1.4 lenses are rarely very sharp in the corners. Dunno about Canons, but Nikons don't have focus points right into the corners anyway, they're all clustered not far from the centre, even the outermost ones. Within that area, the shift in focus is minimal, and easily corrected - it only becomes significant if there is something that is critical focus like an eye right towards the edge of the frame. If there is, then the best way and most accurate way to focus is manually, judging it by eye. Off-centre focal points won't give you the right answer anyway in that case, they simply don't go far enough out.
There is a reason why so many of the best top end pro cameras don't bother with multiple focus points - they're really a toy, of marginal use. If they're a toy that you happen to like and find of some kind of use, then play away with them, there's no problem with that. But all this armchair theorising on this thread about not being able to focus with centre focussing is laughable.