Smok x cube 2

So I recently bought an x cube 2 from a buddy and he was telling me a bit about the features and things it does. He also mentioned something about not vaping on a resistance less than .5 with an RDA and I can't figure out why that would be. I tried looking up info on that to clarify but can't find anything. Does anyone know why?? Or if he was completely wrong. Any help???