Oops, forgot the other reason for clean-n-strip. Firstly they remove
less metal, but secondly the abrasive particle size will get into the
rust pores & pinholes to remove millscale and rust much more
effectively and they leave a very polished surface.

If you are applying an extremely high content zinc coating this is
important as you really need a Sa2.5 finish (walnut/plastic blasting),
but when done it will electrochemically counter corrosion particularly
"pin hole progression". Car metal that is not zinc protected will
pinhole extremely easily and once it does the perforation spreads very
rapidly indeed, it is a down of the very thin yet high strength steel
alloys used.