At the same time they really don't have to offer coupons to use but its something they do. I think personally its to compete with rockauto prices..usually everything comes out to what RA offer it for if you use a code. Personally I don't like to wait and pay for shipping so 99% of just get from advance.
Retailmenot.com is your best friend. No need to wait and use those $5 off coupon they tend to send in the mail often.
I just bought around $160 worth of stuff for around $100 or so and walked across the street and picked it up. Sometimes I split up the orders to save more just depends on what kind of codes are valid at the time.