For developing a mobile app, there is a choice of storing usernames and password data in the device itself, or in a server (user will be authenticated to a server). Other than possibly the user have to manage multiple passwords if he has multiple devices, is there a drawback for the former choice? Also, the app is supposed to connect to internet anyway, so "no internet connection" is not an issue.
You need to clarify your question to get a more helpful response.
Here's the generic answer: storing authentication credentials on a device puts those credentials at risk of offline attack. If a device is responsible for saying it is authenticated, then the somebody may spoof it.
Credential caching is not without merit or precedent. Windows systems perform credential caching for network-disconnected logins.