If you are on Android, the benefit of the mobile website is for those with multiple devices, because you can use the site on your phone to install an app on your tablet. Of course, that may not be the most widely used case for the site. A bigger benefit is finally being able to browse the Devices section of the store, which has always been absent from the Android app. But, being able to browse and buy hardware through the mobile website isn't just a benefit for Android users. Maybe you own an iPhone, BlackBerry, or Windows Phone and you're looking to make a change. Now you can browse to the Google Play Store on your device and pick up a Nexus or Google Play Edition phone as a replacement.
The design of the Google Play website looks essentially like the store itself, complete with hamburger menu and all. The site isn't quite as smooth as we expected, there was some lag and hiccups, but we assume it will get better as time goes on.
source: Google Play