Snapchat launching Lenses for desktop in short ‘a free application designed for desktop that invites anyone to experience the fun of Lenses while using their computer’ this means people don’t have to use the Snap App to use Snap Lens or filters. People can add lens to other forms of video like live streaming or their videos.
The reason why this is a big step for Snap as they need to evelove as platform not just an app to ensure their userbase grows. At first this will be a niche product for Twitch/Mixer/YouTube streamers but as more deveolpers tap into this platform (throught he API) they will be able to find all diffrent type of use cases.
More info here