"Almost every modern string is way stronger then needed. Just use that many strands which give you the right diameter and feel you're looking for."
What Falk said, far more succinctly, is that we use more strands so that we don't slice our fingers off, and so that the nocks fit properly. Thicker strings are a bit softer in the bow's nocks as well. The lighter the string, the more excess energy (that not imparted to the arrow) must be absorbed by the limbs of the bow and your hand. It is all a balance.
Killdeer