I've noticed that setting the lighting mode to shadeless in PBR disables some material channels. In my case I wanted to use my baked lightmaps as occlusion maps but I was unable to do so.
Separating diffuse colors or textures from the lightmaps has some benefits. It makes it possible to tweak the diffuse in the sketchfab editor without having to redo the lightbake. But most of all it makes it possible to do this through the API in a configurator. You could have a nicely baked model while being able to change the color at the same time without the need of having to bake a texture for each color variation.
Is there a way to have the lit lighting mode and have access to the full PBR shader?