Unlike the volume spacers that come with your Fox or Rockshox these "foam" pills offer a different level of tuning to your spring curve. Typical solid spacers reduce the volume of the positive spring and can often produce a harsh ramp up at the end of stroke not allowing your fork to get to full travel.
The Neopos produces a much more linear spring curve, while still allowing the fork to ramp up and offer mid-range support. Lots of R&D went into these and allows the them to compress slightly the deeper you go into your travel so there is no harsh ramp, but still offers bottom out progression. They have a set rate of compression and expansion allowing for a smoother spring curve. You'll be able to run less air pressure which gives more small bump sensitivity without forgoing mid-stroke support.