You have more to gain by using volumes for splitting inserts and components vs. parting surfaces. I describe it to people this way: Imagine you have a cavity and core set on a bench with each half opened up facing you. If you were to spray the surfaces with blue layout dye, the blue surfaces would represent where you would use parting surfaces. Any core pins, insert, slides, etc. you would use volumes. The benefit of volumes is they are capped on the ends automatically, they merge automatically (assuming you stay in the parent volume for subsequent features you add) and can use depth references that are non-parallel to your sketch plane, where a parting surface needs a depth reference that is parallel, and if you want it capped you have to set that option. Keep your parting surfaces as simple as possible and let volumes capture the more complex areas of your split. I see users go through the effort to copy ref part surfaces and use them for their parting surfaces and volumes and in most cases this isn't necessary let the ref part drive as much of your split geometry as possible, keep surfaces and volumes simple. I don't have a good example of this handy, but if I run into one I will do my best to remember to share.
