This optimizes a GLTF file that was exported by blender (or similar) by de-duplicating buffer views (i.e. chunks of bytes) that are equal and removing redundant accessors.
For example, 100 cubes of different scales/materials/rotations/etc should all end up using a single BufferGeometry in ThreeJS, which isn't the case with current GLTF exporters in Blender and parsers for ThreeJS.
In scenes with a lot of instancing, it can dramatically reduce total file size as well as render performance. In one test scene:
Before: 4.8MB file size, 832 THREE.Geometry instances across 832 THREE.Mesh objects
After: 661KB file size, 13 THREE.Geometry instances across 832 THREE.Mesh objects