Parametric Primitives allows you to create easily dynamic primitives, as
Sphere, Cube, Plane or Cylinder without importing assets!
You can change in real time and runtime :
level of subdivision, alignment and normal direction of each primitives.
This can be very useful if you want to, for example :
Prototype a game, making billboards, adapt the polygons number considering the targeted plateform, skybox, heightmap, bending and so many other applications!