Why are they using Clamp here?

I’m learning Unreal Engine and now I’m working on a Post Production material.

This material was in Content Example. It’s M_HIGHLIGHT material, and you can find it at github.

My question is about this three nodes:

Why are they using Clamp here? As far as I now, Clamp will always return 2.

Why to use ViewSize here? Does ViewSize could return a value equal or less than 1?