White label integrations.
You are your own brand. Telling your customers to set up third party shipping and OMS accounts is ok to get started, but not great for scaling and professionalism.
Your own Shopify App: How can your customers get started? Easy! Just tell them to install your Shopify app and they will be ready to go.
Major Marketplaces: Your customers are probably also on Etsy, Ebay, and Amazon. No problem! Wherever your customers are, there is an integration that will bring their orders directly to you.