Why is it needed to set a "root" for an object?

I don’t think it’s possible to have an actor with out some kind of root component. Actor are object’s that can be place in the world, however actor don’t contain any transformation of their own. Scene components are the things that contain transformation so when you get an actor transformation you are actually getting the world transformation of it’s root component. You have to set a Root component because an actor can use any type of component for it’s root.

Hi, I have just watched a tutorial with C++ scripting, that showed the basis.
Why is it needed to set the root apart and manually? I mean, is there any circumnstance where you may choose to have an object without a root? If yes, when?
I understand it is necessary, but I can’t understand why it isn’t included in the class of an Actor already…

Thanks but still I can’t understand fully.
I come from a 3D graphics context, and in those context each mesh has an origin. It isn’t a solid element, but it is represented with a little circular sprite, so that you can see where the root is, and move it eventually. It is like a hook from where the mesh takes the relative origin to do rotations, scale ecc. So it’s not a solid stuff, it’s just (I think) an array with 3 coordinates XYZ and nothing else.
So what are the “any type of components for its root” that an Actor may use?