It comes down to common sense guys, a little experience is what it takes also. I sand blast a lot of parts, but never a large panel, hoods, decks, doors etc.. I blast firewalls, door jambs.inner structures, rockers. bumpers. floor boards, inner fenders, cowling ,tailgates, windshield posts, frames and suspensions etc.
Last year when I was doing my elcamino, I was using a small spot blaster to clean the windshield pinch weld area, the hood had a couple of scale rust spots the size of a quarter and I hit them with the little blaster, they must have raised a 1/4 inch.
It took me a week to fix that dang thing.
Like the rest, I have seen many parts and whole cars ruined with a sand blaster, but I blast every thing I can,t sand easily. I shoot at an angle, never 90* and use a silica sand. I also try to keep the nozzle as far away as I can.
I have blasted lots of early rod body shells with no problems.
You just need to know what you can blast and what you can't.
It's like any other tool, just use it wisely.