I was surprised to not find any discussions about the glTF format here on the Sketchfab forum. The short version is as follows:
glTF™ 1.0 (GL Transmission Format) is a royalty-free specification for the efficient transmission and loading of 3D scenes and models by applications. glTF minimizes both the size of 3D assets, and the runtime processing needed by applications using WebGL™ and OpenGL®-family APIs to unpack and use those assets. glTF defines a common publishing format for 3D content tools and services that streamlines authoring workflows and enables interoperable use of content across the industry.
I sincerely hope glTF merits inclusion in Sketchfab's already impressive list of supported formats. Personally, I strongly wish to see glTF eventually dethrone FBX as the de-facto 3D exchange format. It's a long shot, and it'll take time, but Khronos has a pretty decent track record with these things. It also seems like they learned a lot from their mistakes with Collada.
With Sketchfab having recently implemented a fully functional FBX importer with support for animations, I'm curious what the devs think of FBX. For what it's worth I think the consistency the format has brought to the 3D (in my case games-) industry is laudable. That being said, I've talked to many developers who've had less than pleasant experiences with the format. (example).
The benefits of glTF as an open source format with an open spec should be fairly obvious. If they do a good job getting more adopters on board, who knows; maybe in a couple of years Sketchfab's go-to format for animated models could be glTF instead of FBX