Taurine- Take It
Part of the reason could very well be the fact taurine acts as an osmolyte and exercise can deplete it to varying degrees. While you can't acheive superphysiological levels of taurine as shown in Galloway 2008 you can certainly offset it's depletion while training through supplementing it before or during training.
In general though, I do think it helps maintain electrolyte balance and fluid balance as shown by Narada 2004 which could help in endurance leves and even increasing force contraction potential alluded to an in vitro study by Goodman 2009. All of these factors added up definitely point to the efficacy of taurine supplementation and back-up the in vivo results in humans shown by Zhang 2004 which showed oral taurine attenuated exercise induced DNA damage and increased exercise capacity in cyclists.
Yatabe Y, Miyakawa S, Ohmori H, Mishima H, Adachi T. Effects of taurine administration on exercise. Adv Exp Med Biol. 2009;643:245-52.
Taurine concentration in rat skeletal muscles after endurance running, with and without taurine administration was studied. Taurine concentrations in skeletal muscles was significantly decreased in exercised groups without taurine administration. However, taurine administration reduced the decrease of taurine concentration in skeletal muscles in exercise. Oral administration of taurine has effect for maintaining taurine concentration in skeletal muscles in exercise. The duration of running time to exhaustion of rats, with and without taurine administration were studied. The duration of running time to exhaustion was significantly increased by taurine administration. Oral administration of taurine increases the ability of physical endurance. Rat urinary excretions of creatinine, creatine, 3-methylhistidine (3-MH) after treadmill running, with and without taurine administration were studied. Rat urinary excretions of creatinine, creatine, 3-MH after treadmill running was significantly decreased with taurine administration. Taurine administration was considered to reduce the exercise-induced muscle fatigue.