From http://www.babycenter.com :

“Now’s the time to help your baby develop equal strength and flexibility on both sides of her body. How? It’s easy: Alternate which side you breast- or bottle-feed on, and place her head at one end of the crib one night and at the opposite end the next night. Both techniques will help her get comfortable turning her head in both directions. That full range of movement leads to greater muscle control, which she’ll need to master eye-hand coordination sometime around her ninth month.”