The downside is that Shopify is only appealing for people who have physical or digital products to sell and have a need to set up a Shopify store, including site hosting, payment processing, and all the other services offered by Shopify. This can significantly narrow the appeal for this affiliate program. But if you can distinguish yourself by educating people on how to use Shopify, how it can benefit their business, and/or make them money, you could potentially big money via the affiliate program. Add in the 2 x monthly fee commission rate, and landing just a few sales of their mid-tier and top-tier products can result in significant earnings.
The phrase, "Affiliates are an extended sales force for your business", which is often used to explain affiliate marketing, is not completely accurate. The primary difference between the two is that affiliate marketers provide little if any influence on a possible prospect in the conversion process once that prospect is directed to the advertiser's website. The sales team of the advertiser, however, does have the control and influence up to the point where the prospect either a) signs the contract, or b) completes the purchase.