Local control allows for local preferences and a faster response to local problems. A 90-mph speed limit makes more sense in Montana or Arizona than in Delaware or Connecticut, for instance. It's also a shorter trip to the state capital than to the national capital, if I need to take care of something. On certain issues, different states want different rules. For instance, same-gender marriage might pass in Maryland, but it won't pass in Mississippi. If it's decided at the state level, the people in each state can decide for themselves what the standard will be. (The same applies to abortion.)
