The Anderson Swing Weight Explanation
The debate is almost wholly focused on the overall weight of the bat. There are two schools of thought: swing the lightest bat possible to increase bat speed or swing a heavier bat that increases the available momentum. Both theories are designed to maximize the velocity and thereby the distance of a hit ball. Both theories are based in sound thought as far as they go but both are only part of the picture.
The Drop Weight myth holds that lighter is always better. The problem is that in the guise of simple marketing the bat-buying public was sold this fable by the bat manufacturers with no regard to the disservice it would provide to the young player. The advent of stronger aluminum alloys and better manufacturing processes made lighter and lighter bats possible. As these lighter products were brought to market, the drop weight was a convenient way to differentiate the different new models as the bat weights dropped.
For many years, "new and improved" in the bat industry simply meant that the bat was lighter. Selling the ever-lighter bats as the magic pill that cured every hitter's ills was like shooting fish in a barrel. However, the cure is likely to kill the patient, especially later in their career where all roads lead to a heavier bat.
The delusion that - in terms of overall weight - lighter is always better is simply not true. There is such a thing as a bat that is too light, and - part of that same reality - a heavier bat can be made to swing as though it were lighter.
Considering the physics and physiology involved in the ball-bat collision, there is no real data to support the better performance of a lighter bat, and in fact the opposite is true. Simple application of Newtonian mechanics can supply correct approximations on the effect of weight at each level, but precise details demand the use of continuum mechanics. However, in the interest of keeping Newton out of the debate, it will suffice to say that if all else is equal a heavier bat will, without question, hit a ball further.
A light bat is significantly more important to mid-swing adjustment and more consistent contact rather than more powerful contact. The human musculature has its own speed limit; meaning, just like foot speed, there is a limit to how fast your fast twitch muscle fiber will allow you to move. That means that a bat can be lighter without positively affecting the swing speed. This muscular speed limit allows for the possibility that a bat can be too light.
The primary limitation in bat speed is musculature, and if willing to work anyone can overcome a two or three ounce difference with simple repetition. If you add resistance in those repetitions, not only can they overcome the weight but they can also improve the maximum speed that the musculature can achieve. In the space of just a few weeks a player can adjust to what is viewed as a significant difference in weight based on the myth. This is all assuming that the player has good mechanics. Success that is solely dependent on an ultra-light bat is usually a masking of poor hips-and-hands-to-contact mechanics. It is a Band-Aid, not a fix.
Enhancing the more important mid-swing adjustment to achieve more consistent contact can, without question, be done substantially without lightening the bat.