What got me started on this was WhatsApp. A (non-IT) friend suggested it so we could communicate cheaply while she was abroad. When I downloaded the App it asked for access to my phone directory - which seemed reasonable in view of its purpose. The next thing I knew it had copied all the entries in my phone directory to its database. I did not consciously give it permission to do that. I had assumed it would ask me on a case by case basis whenever I wanted to contact someone.
I deleted the App and changed my phone number.
...R