Skin.ini is basically storage for variables that overrides the variables in RR.ini for just that skin. If you only use one skin, it's kinda unnecessary/redundant from a end-user point of view. If you use more than one skin, it can be used to differentiates the setting for the different skins, i.e., I use different sizes and locations for YouTube videos, but the general settings are the same. So those that differ go in skin.ini and the rest are in my RR.ini.
The real fun in in the ExecTBL.ini. Skinners use skin.ini to insure the programming they put in the exectbl.ini uses appropriate variables for their skin, but if you use the same programming in more than one skin, it's best to save those variables in RR.ini. For example, DFX Weather allows several cities be saved as buttons and I want those same cities listed in my other skins that have that option; therefore, those variables need to be saved in RR.ini. And to do that, you're gonna have to modify the exectbl.ini in those skins. Full circle - start deciphering exectbl.ini files to really learn how to make RR do just about anything imaginable.