My guess is for a sort of absolute positioning as opposed to the relative positioning of an optical mouse.
A mouse produces deltas relative to your previous position, while the bar codes are always in the same place.
The problem with relative positioning is that even a small inaccuracy will accumulate over time, resulting in edges being off in the end.
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Why do you need to put barcode markers on the surface? What's wrong with optical mice?
My guess is for a sort of absolute positioning as opposed to the relative positioning of an optical mouse. A mouse produces deltas relative to your previous position, while the bar codes are always in the same place. The problem with relative positioning is that even a small inaccuracy will accumulate over time, resulting in edges being off in the end.
because optical mice aren't very accurate on a scale larger than one motion of a few inches