When is it good to Sand/ Media blast your car?

I had both my cars media blasted completely. One car is from south carolina, the other from arizona. They have no body rust and the media does not remove body filler like sand does. That helps when trying to find bad spots. media doesn't break into the metal so surface rust wont happen overnight like with sand. My car didnt get put in primer for over a year and the paint turned out beautiful. It was a lot of work but I am glad I did it this way.