In my experience, if done correctly, plants show no signs of slowing growth. They actually grow faster better because your exposing valuable growing tips(colas) to more light, stimulating growth. It doesnt take a rocket scientist to realize that shaded branches stop growing and eventually die off. Trimming or tucking the shading leaves stimulates bottom bud growth.

-If its your first grow....dont touch the leaves.
- If its your 4th grow and your tired of the god damn scraggly piece of shit buds on the bottom, either cut them off or remove some fan leaves and get more sun down there. Not having the sun moving across the sky is a burden us indoor growers have to bear.