Therefore, each quality must be addressed, in tandem, during drills. It is not enough to practice swinging a bat fast, by itself. It is not enough to practice making contact with the target, by itself. The two objectives must be coupled in order for maximum achievement. Aim to make every swing fast, and in particular focus on increasing the speed of your swing after contact with the target. Accelerate to completion.
And, swing at a target. Dry swings (without a target) are more of a conditioning tool and may have a purpose for some batters; but swinging a bat in and of itself will not make a hitter great. A hitter must swing at a target, either a stationary one on a tee or a moving target as thrown, tossed or pitched. Greek historian and author Xenophon said, “Fast is fine, but accuracy is everything.” Combine the 2, and become great.
From November 2010, http://raisingahitter.wordpress.com