In the Settings menu and the Apps sub-section of it you can check what permissions have you given to each app, both OS ones and 3rd party ones. I usually just give the Apps enough permissions to work properly for what they are supposed to do. For example, I wouldn't give a gaming app the permission to access my phone calls history, contact list or the camera and microphone. In contrast, I would give the permission to access and freely use the microphone to an app that is entirely based on that function - for example, Skype (for calls and such).
As I said, you can check for each individual app, both system or otherwise, in the App section in the Settings menu of your phone. Even if you allow all apps all kinds of permissions, as long as you download apps solely from the Google Play Store, you would most likely be okay. The apps would just collect more advertising data on you, that's all.
Edited by Just_One_Question, 19 July 2017 - 11:58 AM.