They don't "take plenty of nutrition away from the plant". They gather the sun's rays which is necessary for photosynthesis.

They also shade the fruit from sunscald.

This post was edited by robeb on Mon, Jun 3, 13 at 18:43

Yeah, the plant's health is dependent on the leaf branches for its growth energy derived from photosynthesis. Pruning a few select branches is one thing, cutting most of them off is something else entirely and highly detrimental to the plant.

Dave

Here is a link that might be useful: How photosynthesis works