Many businesses ask you how you hear about them, when you first visit them. Because the data is important for growing their businesses.
OK, you have an android app. Aren’t you interested in tracking how the users find you? For example, via facebook posts, tweets, forum threads, or partners’ blog posts?
How to track it? The answer: use the INSTALL_REFERRER broadcast.
How does it work? You pass encoded data to Google Play app, via a special link query parameter (i.e. referrer). Once the users click the link to Google Play store, and then installed your app, Google Play sends your app a broadcast, passing back the referrer data.
You can put in many information into the referrer query string, such as ad campaign name, channel names, affiliate names. You may put in other data too. Use your imagination. Of course, do not put in sensitive data like your salary amount.
For details, visit Campaign Measurement – Android SDK.