Apple might claim that it makes it easier for you to download all of your apps onto a new device or some such nonsense. The reality is that it is primarily for

Apple might claim that it makes it easier for you to download all of your apps onto a new device or some such nonsense. The reality is that it is primarily for Apple's benefit, not yours: Apple wants you to set up a billing account with them (even one without a current payment method) in order to make it easier to sell you stuff in the future, and they also want to target you with advertisements in the app store based on the apps you've downloaded, etc.