the system is designed to ask the first time the app is launched. if, later on, you change your mind
regarding the app's permissions, you change them in the system's settings tab for the app. you don't
have to uninstall and reinstall the app. the alternative - forcing the user to grant or deny permissions
every time the app is launched - was not implemented (an app may require access to more than 1
feature). this would prove very annoying very quickly if i wanted to take a photo but had to answer
questions relating to camera, gps, phone, photos, contacts, etc every time i launched the app. ask
me once, and if i want to change something later, i can change a particular permission in the app's
settings. it is the developer's job to inform the user regarding an app's permissions and how to manage
them. this is covered in google's documentation relating to runtime permissions.