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

Heck,if that's all there is just wire brush the loose stuff off,apply por15 and forget about it.

With my Dart,Im getting blasting in the spring and we will see what is left,lol..pretty bad but I can weld and hand form metal. My buddy Chris is blasting for media cost only,but even so media will still cost $300 -$600