Originally Posted by
Sixty Fiver
When you set up a bike's derailleurs you dial the derailleur's position relative to the cog set to maximize the performance of the shifting system and if you re-install the wheel in a different position this will affect the fine tuning of the rear d and change the chain tension.
This is the only answer I've heard that makes any sense. The changes in wheelbase would be to minuscule to really make an impact, and proper alignment could be more easily achieved by simply pulling the wheel to the back of the dropouts.