According to a post on Apple’s Developer website, it reads, “We’ve worked closely with leading developers to create a solution for reducing customer churn while improving the experience for auto-renewable subscriptions. With the new grace period for unsuccessful auto-renewals, subscribers can continue accessing your app’s paid content while Apple attempts to collect payment — allowing them time to fix the issue.”
It’s actually not surprising that Apple is doing everything they can to keep customers subscribed for as long as possible. This is because subscriptions ensure a steady source of revenue, versus single one-off purchases. It will also allow Apple to consistently collect their share from the subscriptions without really having to do much.
According to Apple, the grace period will vary from subscription duration. For example, a one week subscription will offer a 6 day grace period, and one month subscription with a 16 day subscription, and so on.