planar and 3d region

Maybe anyone asked for that already, but I can’t find that in the forum.
I’ve little problem to really understand the difference with the planar region and the 3d region… obviouly the difference it is… one in 2d and the other is 3D, but… both nodes works when they’re attach to the peg… then, if the peg is 2D… the 3D region keep been 3D but can be configurated to be 2D, meanwhile if the planar region is 2D, ones that the pegbar is configurated to 3D… then, what is the real difference with the 3D region?
In the perspective windows, actually I can’t see any difference between the both region.
Could anyone gave any better explication because what the Toonboom help says, it’s easy and obvious but, I’ve the feeling that it is not exactly what I see in the perspective windows as a preview…