Certain paid In App Subscriptions may offer a free trial period prior to charging your Account. If you decide you do not want to purchase the In App Subscription, turn off auto-renewal in your Account settings during the free trial period.
Looking at that bit of the terms, this looks a lot like the door is opening to allow what some have held up as the Holy Grail of App Store features: free trials. This is going to be a VERY big deal for people who are already having to maintain a free version of an app separately from the paid version, or have to try to sell people on the in-app purchases.
We haven't seen any of these yet, but hopefully this is an option available to developers that will start being utilized immediately.