You get the ease of use/better workflow (for example, if I want to add muzzleflashes to a composite/greenscreen shot, I simply have ONE project, rather than having to key out the background, render out the project, and then import, add the muzzleflash and re-render).
There's also several exclusive filters that you'll only find in VisionLab - you can also be sure of having access to any new technologies and features, which might not necessarily end up in the Lite and Pro products.
But as well as this, the main advantage (and the reason for the price difference) is that Vision Lab comes with a commercial license. This means that if you distribute something you've created with Vlab, you do not need
to include a credit for FXh, unlike if it was made with Effects Lab or Composite Lab. There are some scenarios where you simply couldn't include a credit (e.g. in a music video or advert), and so the commercial license comes in very handy in these situations.
I hope this clears things up