If you plan to build any kind of platform integration, including a dedicated mobile application, for example, using Salesforce APIs or any you build using Apex, you will need to create and package what's known as a Connected App. This allows you, as the ISV, to set up the OAuth configuration that allows users of these integrations to connect to Salesforce, and thus, your logic and objects running on the platform. You don't actually need to package this configuration, but you are encouraged to do so since it will allow your customers to control and monitor how they utilize your solution.