Closed planar curves vs closed curves


What is the difference between Closed planar curves and closed curves? with closed planar curves we can connect it straight to surface component and it creates surfaces. with closed curves it give red component by saying “curve cannot be converted into surface”. Another option is to use Patch component. But i would like to understand them and how their logic goes on.

Here is small example. (138.3 KB)

as the name specify Closed Curve on plane (closed planar curve)
closed curve dont have to be in a place it can be in 3d space too