I think you misunderstand.
I am talking specifically about the early stages, from seedling to veg. IF you keep your soil moist, the roots do not grow as much because the water is ALWAYS right there. This slows growth, it does not accelerate it.
When you allow your soil to actually become dry, the roots will go "Where the hell did my water go?! I must go find some!", and they will. Minimal watering during seedling stage encourage root growth, which obviously allows the plant to suck up water even better.
I've already done what you've suggested. I've let seedlings be constantly moist, and I've let them dry out. When I let them dry out, my plants are easily DOUBLE the size of the seedlings that were constantly watered.
NOTE, I am talking about the SEEDLING to VEG stage, NOT the entire grow.