With the advent of the Google search button to download and test mobile applications, indexing has become more urgent than ever.It “sees” the application from the inside and makes it available to the Google search engine. The user who installed the application on Android or iOS, can open it directly in the search results. When you re-request Google will automatically prompt and return the client to the application.
How can this be useful for application developers and companies?')
Increase the number of installations and conversions.The user is looking for information similar to the contents of the application, and this application is shown to him, thanks to matching requests. The search leads the user to a specific page in the application that answers his question.
Increase the number of active and loyal users.The user is looking for information through the application, for example, delivery from a restaurant or a taxi. Closes the application, and after a couple of days returns to the Google browser. The search engine when entering the request gives the user a link to the application. The user returns to the application.

In recent studies, Google says that on average, open only one of four installed applications. Keeping users in such conditions is an important factor.
Indexing links the closed ecosystem of applications with the dynamic linking system of the mobile Internet and actually blurs the boundaries between them. This is evident in mobile data streaming applications.
There is another important moment for developers and marketers.
To determine the ranking in search results will be taken into account not only the site, but also a mobile application.Here's what Google
says about this: “For Android and iOS users, indexing applications will affect the rating regardless of whether the user has the application installed or not. This means that if your application is indexed, Google will use the content of your application, not just the content of the website, for ranking. ”
According to Searchmetrics , 70% of sites with an application on Android and 81% on iOS, still do not use the API API for indexing applications.
This means that those who use deep links to connect with the results of mobile search will now have a new, serious channel for distributing applications. With a minimum of competitors. On condition of current, user-optimized content and proper technical implementation, of course.
To add your application to the Google search index, you need to perform 3 steps: 1. add link support to the application; 2. Embed deep links into the application; 3. Test the work of the links.
Google gives
detailed instructions on how to implement an API.
And below is a survey on the topic.