ā€‹Unrestricted range of motion in the shoulder allow for a number of factors:
1. Less carry over into more sensitive joints.
Whatever range is lacking in the shoulder will have to be picked up somewhere else to make the swing work. This can be overstraining the hip, knee, ankle, ribs, lower back and even neck.
2. More wind up, thus more power.
Like in any sport that involves accelerating an object, large range of motion allow more control, as well as precision and power.
3. Health and Longevity.
The less restriction there is in a joint, the less wear and tear it has to absorb. Flexible joint means, possibility of playing the game longer, while enjoying it more.