This way developers who are not running Windows 10 can test any site with the latest IE without the need to run a new OS or heavyweight virtual machine on their device.
RemoteIE and Azure RemoteApp are in preview and developers may experience service interruptions. The service is only for testing and performance will not be the same as running IE natively. Also developers should consider what microsoft noted on the blog: "Sessions are limited to conserve server resources. Sessions idle for 10 minutes will be logged out and no session can last more than 60 minutes – you’ll need to start a new session"
In the end Microsoft provides a reasonable compromise and RemoteIE cand make the life easier for developers who want to optimize the content for all the modern browsers. If they will use the service remains to be seen. To get started developers can go to https://remote.modern.ie and download the Azure RemoteApp client for a specific platform.