iOS - store data locally ONLY

I'm new to iOS development or any native mobile app development and I want to confirm my understanding of database concepts for iOS apps.

My understanding so far is that, for apps like Facebook and Twitter, their central data resides on their web server and their mobile apps just interface and communicate through the API to keep them in sync.

Another type of app could be that it doesn't have any web presense and only started as iOS app. Therefore, its data gets stored only on local storage of a user's device and iOS ORM - Core Data maps with sqlite for this local database.

Is my understanding correct, especially on the latter part?

My app will fall into the latter category and just wanting to know if this is a standard practice to not incorporate data connection over the wire.