How Does WebGL Handle Directional Lightmaps?

I heard WebGL doesn’t support directional lightmaps. I don’t know how they work - does that mean you have to bake scenes in Non-directional mode when deploying to WebGL? Or does baking Directional just store more information than what WebGL will use, so when deploying to WebGL it includes the necessary non-directional data?

Would there be any disadvantage of deploying WebGL after baking directional vs. non-directional lightmaps?