The average Sprit customer is price-sensitive compared to a Delta customer and will have lower spend per basket (or just rely on vending) than a Delta customer might bring overall to your business.

(This is ironic, because generally every time I line a low-cost-carrier up against a mainline airline like Delta, once the baggage is added that is generally free on a mainline the ticket cost is within $50-100 of each other, and worth paying the extra few bucks to not have as much hassle.)