The main benefit of an Onelink from Onelink.to is that it simplifies app downloads, removing the need to consider what device someone is using. Onelink.to will automatically send each user to App Store or Google Play etc, depending on what device is being used. On top of that you get a dynamic link and QR code, and statistics.
The use cases are numerous, but the most common are:
Email and SMS marketing and direct messaging
Web based banner or link advertising using shortlinks
Printed advertising with QR codes, in newspapers, outdoor advertising, etc
Digital signage advertising with QR codes
App download shortcuts in printed material (manuals, product sheets, etc) using QR codes