With 80% of our neuro processing information coming through our eyes, it stands to reason that both eyes should be operating at optimal levels. If we get poked in the eye, our depth perception is off as well as our visual acuity while the damaged eye tries to recover the one remaining good eye tries to take over. Binocular Tracking remains the most effective form of processing information for human beings.
When softball (and baseball) players are up to bat, they eyes are trying to gauge trajectory and motion. When the athlete is looking over their shoulder, some are actually using monocular vision because their nose is getting in the way of seeing the ball binocularly. The introduction of the open stance gave hitters more processing ability, but slowed their swing down. The semi-open stance give the players the best of both worlds with Binocular Tracking and speedy enough reaction time to process the ball.