Second, about a minute after liftoff, all atmospheric forces on the vehicle reach their peaks. Rotating a shuttle right after launch puts the vehicle into a position that helps reduce stress on the orbiter, especially on the wings and tail.
Finally, the roll maneuver enables a shuttle’s pilot to see the horizon. This provides an important reference in the event controllers need to abort a mission during launch. — Bill Cooke, NASA’s Marshall Space Flight Center, Huntsville, Alabama