Please find my first digital prototype at https://www.flinto.com/p/db9835a0.
Paper prototyping helps me realize that the bottom navigation bar should clearly indicate all the views available in an app. A user should always stay on one of the views. It becomes obvious that a constant navigation bar will keep the interaction flow, i.e. avoid that a user got stuck at some point in the app.
Apart from this, I do have a feeling that paper prototyping for mobile app is becoming less efficient compared to evolving, convenient digital prototyping tools we have today. Because the mobile application is a species born from the very medium of digital screen, a traditional medium is not capable of many of the interactions the mobile screen cultivates.