If UVB rays help create Vitamin D why wear broad spectrum?

Bob B Asked: If UVB rays help create Vitamin D why wear broad spectrum?

I've recently learned that UVB rays help produce Vitamin D by reacting with cholesterol. UVB rays are also the cause of sunburn so I can see why someone would want to wear a "broad spectrum" sunscreen that protects against UVA/UVB on a very hot day or at the beach. But on a daily bases, going to work, going for a walk ect., why would one want to wear a broad spectrum sunscreen if it blocks against UVB, the ray essential in converting cholesterol into Vitamin D?