Sticker apps are nice, but they're not particularly interactive. You can build far more interesting and interactive applications for iMessage through the Messages framework. Some of the larger, well-known apps on iOS have been able to implement iMessage extensions that make sharing content from their apps easier. There are even people that have built games in iMessage! The Messages framework allows developers to build a wide range of extensions straight into the Messages app.
You have just seen how you can build sticker packs and how you can create a somewhat customized sticker pack by picking the app template instead of the sticker pack template in Xcode. You haven't gone in-depth into the different life cycle methods that Xcode generates for you when you create a new iMessage app.
To go into more depth with the Messages...
