"When you buy something on Pinterest, you'll need to share some payment and contact info with us so that we can complete your order. We'll save this info so you don't have to type it in next time you make a purchase. We'll also share this info with the seller, and they'll treat it as if you bought from their website directly."
Essentially Pinterest is acting as the middleman between the buyer and seller, and you'll be able to save payment information should you happen to purchase numerous pins and don't wish to re-enter the same information. As well as the new payment feature, Pinterest will also be making some changes to Promoted Pins:
"We also hope to make Promoted Pins even more relevant and useful to Pinners like you. For example, if you purchased a camping tent on Pinterest, we may show you Promoted Pins for other outdoorsy products."
As well as highlighting some upcoming changes, these revisions to the policy also mean we're drawing close to the update, which should start rolling out soon. We'll be sure to let you all know once the release is approved and live on the App Store.