Discount codes are sick. I want to buy stuff for cheaper.
Sometimes they are not put out for sick reasons and they act a lot like affiliate links, where a manufacturer, retailer etc, will pay someone to connect customers to them. Discount codes can help sellers directly track how a consumer got a sale and will give the person who encouraged the sale, some money for it.
Having a financial incentive to sell a product, may incourage someone to promote a product they would not otherwise. I have not seen this much in longboarding, but be wary just in case.
I see this in gym content all the time.