Question: The [Apple docs](https://developer.apple.com/library/content/releasenotes/General/ValidateAppStoreReceipt/Chapters/ValidateLocally.html) on receipt validation say to perform receipt validation immediately after launch. This amounts to checking for data at the path returned by `[[NSBundle mainBundle] appStoreRecieptURL]`, refreshing via `SKReceiptRefreshRequest` if it's not there, and validating it. The aforelinked docs reference both iOS and macOS.

Is it actually *necessary* on iOS? If so, why? Is it to prevent users from using my app on a jailbroken device, or without having bought it from the app store (in which case I probably don't care if my app is free)? Or does it have implications for other operations like restoring or validating in-app purchases? For example, does the receipt data have to be there already in order to validate a transaction for an in-app purchase?

Note: I am not using in-app subscriptions. I have in-app purchases, but I don't use the receipts from them after verifying them and recording the purchase server-side.

Answer: 
The reasons I would give are:

1. The user can change their product if you are using subscription groups from outside of your app.
2. An auto-renewing subscription can renew outside of your app.
3. The app does not receive transactions initiated outside of the app until the app restarts.
4. The user can make purchases on another device using the same appleID whilst outside of your app on the current device.

Within our appDelegate:application didFinishLaunchingWithOptions we initialise a class that calls
[[SKPaymentQueue defaultQueue] addTransactionObserver:self];
to monitor for purchases initiated from within the app.
It's not necessary, but beneficial for the following reasons:

1. You'll always get the definite set of purchased products and not require the user to manually restore the products.
2. You have (limited) fraud protection, especially if you combine local and remote validation.
3. It's way more simple to compute the expiration date for automatically renewing subscriptions using the recipe.