If they are undocumented then they do nothing except what the examples show. (well programmed unix things, like Motif, have a variable exposed for anything that could change, and three ways to get at changing that exposed variable - almost to the point of monotony - yet ending up a compact program)
I liked earlier versions that had all .nb (or Put or Needs) for all kernel libraries.
However that makes it easy competition to steal and offer the same product at a lower $ (please internationalize that if need be).
Wolfram is outreaching to community and does answer such questions about some given function when the need arises though.
In my case I made a raytrace front end for mm and got really burned because many functions not only are undocumented but do not give Graphics output: they ONLY give opengl output internally so to replicate them it meant writing a new function that does the same thing for each one.
I probably should have asked wolfram a few questions to save time instead of doing certain things "the hard way". And that's my point. You have only to ask them.
((No matter if I went forward I would code it all in MM anyway, but because mm's 3D has gone new directions that are good but very different from rendering software abilities - i likely won't do it even as a hobby - because then i'd be also coding all of modern opengl use as well as all mm un-exposed things - a bit of a task for one unpaid person i'd say!))
My complaint would be Mathematica is great as a math swiss army pocket knife (the functions allow any specific goal to be achieve without providing a function for every conceivable goal). But Wolfram seems to have paid employees to add many small program functions that do very little (nothing that mathematica couldn't do without them), all in a name. On the other hand my PC is still running fast enough so I can't complain. The addition of Geo and Chem and other things are great.
However your answer may be this (an educated guess). DegreeGraphDistribution[] is used to provide a service to a higher Mathematica function that IS well documented, so you don't need to know how it works, because it is a service function. That's typically the kind of answer I've seen over the years which may apply here.
