The ability to add an app to the home screen is one of many great features of Progressive Web Apps. The same reason why you want your customers to install the native applications, you want your customers to install your web app.
ScandiPWA is promoting the installation of your website within the web UI of the application.
For Android users:
The promotion banner appears on the homepage of your website and gives your customers the ability to install the application directly from there or dismiss the promotions by clicking on the close button.
For iOS users:
Unfortunately, there's no such thing as a native installation pop-up on iPhones, so our visitors might not even be aware of the app's capabilities. Notwithstanding, the promotional banner for the app installation on iOS informs the customers of such ability and instructs them on how to do it. And of course, the dismiss button is also available on iOS.