What is the preload spring on the brake pedal for?

Hi, I just would like to know what the little spring that is i.e. at the end of the Heusinkveld oder SimJack / Simsonn pedals is good for? Is it just a spring to make the first few percent of brake pressure linear before going into the elastomers for a progressive feeling? If I see it right, no such spring exists i.e. in VRS or Simgrade pedals (which don't use elastomers).