The value of hitting the ball hard
Data from MLB indicates that there is separation point for hitters in how hard they balls are hit, or their exit velocity. There have been numerous studies done about weighted bat training, most by Coop Derenne, that support and verify training with weighted bats. My weighted bat thesis and training experience is straightforward to the fact you won't necessarily need to read the studies. Stronger athletes that swing more efficiently create higher exit velocities.
Getting big and strong is easy to understand in theory. Increase your baseline strength in bench, squat, and deadlift using and undulating periodization, and you will be able to produce more power output. Swinging a bat more efficiently is a little more complicated to understand. First, we need to try to understand human movement.
Weighted Bat 101
All human movement is governed by the central nervous system (CNS) of the human body. It acts as the command center for our movements and is responsible for all voluntary movement. It is very adaptable and responds quickly to changes in our environment to accomplish required tasks.
During movement, our body is heavily reliant on sensory information to create a roadmap of our surroundings. This helps us orient ourselves, and create a motor plan to solve the movement task in front of us. Take riding a bike as an example. In the beginning, the task is challenging. Learning to keep the bike balanced as you peddle seems like an impossible task (which is why the most complex movements are determined from a young age, stubborn persistence). But the more acclimated your body becomes to the task, "creating a roadmap," the more the CNS will develop an autopilot for the task to accomplish the outcome.
Now to hit a baseball. It's the most difficult skill in sports, and achieving it requires more than just simple "mechanics." At the beginning aiming a round bat at a round ball and making square contact in fractions of a second seems like an impossible feat. But the more time you spend, the better and easier the task of hitting the baseball becomes. This is the CNS adapting quickly how to do the task. As this process becomes easier, the hitter’s CNS can stop making changes because the body has developed a roadmap for the execution of the movement. This roadmap then becomes a permanent fixture in the player's brain and thus, efficient or not; it is there unless a new challenge is presented to the system.
The new challenge becomes a different weighted bat. This wakes up the brain and forces the CNS to stop using “autopilot” so that new, better roadmaps are created within the brain to accommodate the change. Think of your practice process as a hitter; you go to the cage, hit some balls off the tee, do some front toss, maybe take some BP, and call it a day. Not only is this boring to you, but it is also boring to your CNS not evening registering as a slight breeze to a flag on its flagpole (yawn). Now do that same process using weighted bat implements. You now have new sensory information because you are using a heavy (end or knob) and/or a light bat. The CNS must go into overdrive to account for the new variables, and a new, better movement roadmap is created. Effectively you are taking what used to be a two lane somewhat curvy road that your movement plan traveled upon and are turning it into an eight lane super highway. Because the challenge of the weighted bats is new, and the body realizes it's new, additional movement compensations must be made to accomplish the task.
Think of it like this. When the body attempts to apply force, it recruits muscles according to their size and their abilities to produce force. Try this, bend over to pick up a pencil, the body doesn't recruit much muscle and can be done 10,000 different ways. The efficiency of movement isn't the chief concern of the brain at this point. Then Deadlift 500 lbs., the body recruits a lot of muscle, thus needing the efficiency of the movement to be much greater to accomplish the task. So when trying to swing a bat, relatively light (2 lbs.), with your legs, core, shoulders, and arms all at the same time, we are not going to recruit the largest muscles from those body segments unless you have introduced this movement pattern to your CNS using weighted bat implements.
When it comes to accomplishing the task of hitting a baseball in high stakes, stressful, reactionary environment wouldn't you rather have an information super highway to execute movement patterns than a curvy mountain road? I know I would and thus your swing, now governed by intent, becomes the ultimate reactionary weapon ready to be fired in an instant.