I need two 120v, 20A circuits in a storage building that's 150' from the service panel in my house. Is there any reason to not just add two 20A breakers to my service panel, as opposed to putting a 40A subpanel in the storage building? In both cases I think I have to run the same wires: two #10 for hot, one #10 for neutral, and one #10 for ground. The only thing I see a subpanel buys me is a circuit breaker out in the storage building instead of up at the house.