I spent some time last week helping shear sheep at my dad's place. No sheep were harmed in this process. Sometimes they will be nicked by the blades, but it is no different than when your husband nicks himself shaving. Sheep are shorn in the spring to help keep them cooler in the summer. Can you imagine wearing all that wool in 90+ degree weather? Also, a bulky fleece will decrease the mobility of the sheep and they need to be able to move to graze or flee predators. A long fleece can also hinder a newborn lambs ability to suckle the udder.