MAR | 2016
Google automatically sends out crawlers to crawl web sites for new or updated data on a regular basis. This information is then included in Google’s index, which you access every time you make a search enquiry. Indexing is basically Google filling its searchable database full of new data or information. Google can index the content contained within an app, either through a sitemap file or through Google’s Webmaster Tools.
If any visitor searches for data that is contained within an app, and the visitor has that app installed, they will then have the option to view that content within the app, instead of simply on a usual mobile web page.
To let Google index your apps
For iOS you need to set up support for Universal Links. This is what Apple calls HTTP links that have a single URL, used to open both a specific page on a website and the corresponding view in an app.
For Android, implement Google App Indexing by using the App Indexing API and for iOS 9, by integrating the App Indexing SDK.
You should allow Google to index your app because Google itself has stated it is a ranking factor for both android and iOS users, whether or not the user has your app installed. To increase in ranking you should optimize the result by using techniques like SEO etc. Apps also hold a significant amount of data that was going undiscovered. It was a missing piece from the complete customer journey, possibly as profound as visits to retail stores.