This can be used to provide an interactive 3D presentation of your model, scene, or item that users can zoom, pan, or rotate around to get a better view of your submission. Here’s an example from johnskyrim’s Doomhammer, a Skyrim weapon mod:
When preparing the Workshop page for your mod or item, you now have the option to include a 3D Sketchfab preview of your item along with your videos and screenshots.