It all comes down to when you want to pay for your lunch. When you choose to repeat an order, the order is copied for the entire ordering period (semester). All of these lunch orders are then added to your cart, and you must pay for them, in full, at checkout.
Activating your subscription allows you to order all at once and pay weekly! When you subscribe to an order, the order is copied for the entire semester or open ordering period, and you are ONLY charged on Saturday for the following week's order.