The concept of volume charge density is an even distribution of charge over a three dimensional area. C/m^3. However, the concept of electrostatic equilibrium says that all of a conductors charge lies on the surface of the conductor. The existence of one seems, to me at least, to render the other pointless... Anything less then a perfect non-conductor would nearly instantly rearrange the charge towards the surface. So a volume charge density is a purely theoretical construct that will never exist. So any application of it is just in practice to demonstrate the math. Am I missing something?