Most, if not every, Shopify client would create ads showing exclusive deals and discounts. An online ad, like an instagram story or a facebook post, would link to that pdp. In order to increase conversion rates, the client would need to create a link to have their users have that item(s) in their cart or instantly go to checkout.
Creating a link for this requires knowing how to navigate Shopify's API docs, which is a hassle for most. Even educated, imagine having to create multiple links for various offers, custom discounts for each one, item quantity, having a different item. Becomes unbearable.