Most modern cammed sails will rotate fine no matter how much or little batten tension is applied b/c cam pressure and batten tension are not tied together when cams are of the non-compression variety. This assumes the ideal mast. Any variation in mast flex can change the outcome, of course.
Batten tension is necessary to achieve enough skin tension that will allow the leech tension to work as intended. Much of a sail's feel is a combination of skin tension and leech tension. Insufficient batten tension will cause the draft to move up the sail as well as aft. High batten tension often will highlight an asymmetric feel to the sail -especially where the batten tension system isn't compressing from the center of the batten.