Hello
The skeleton is composed of reference elements (such as User Parameters, points, lines, plane, etc.) the topological operations, instead of relying on each other (parent link, child) will rely on these elements which facilitates dimensional modifications and interchangeability of shapes.
Example: we all know how to draw a cube and each CAD software offers several possibilities to build this cube.
But when you want to modify these dimensions, the way you created it will imply the ease of making it evolve.
For example, the support of the sketch, if we have relied on another geometry or on one of the absolute planes, (XY; YZ; ZX) move the base of the cube of this type of ref by (... Several solutions: extruding 2 directions, one of which is in -, or a negative thickness, or a pocket, etc).
One solution is to create a plane that will serve as a support for the sketch, so if you want to move this support (the position of the base of the cube), you just have to move the plane.
It is very easy then, for example, to have imagined that this plan represents the support between two pieces (why not two plates), if we modify the plan, we will increase the thickness of one of the plates and reduce the other.
If we don't know the position of a shape in space or its orientation (we can create a point and then a coordinate system on this point after all that we build on this coordinate system, we will be displaced if we move the origin of this coordinate system. If we are rigorous in these parent-child bonds, we will be able to orient the form 360°.
We can therefore consider the skeleton as an interface of references between the various parts, (in the case of an assembly) and where the search for the control of dimensional modifications.