I get the whole notion it auto sieves out the fines and you can just recirculate the grit forever, problem is as the grit loses its corners it cuts slower and less efficiently, net result is a far more shot peened surface than a blasted one, now that's not say a issue if your simply lightly texturing parts prior to plating or similar or using something like glass beads for part cleaning.
But If your trying to do a surface prep to promote bonding, ie adhesive, paint or powder coat this really starts to impact coating performance. If your using it to strip nasty parts theres also a significant slow down in cutting speed when removing old pain and such too.
To a degree though you can limit the above issues by choosing tougher better abrasives and not using any more pressure than you need to strip finishes. Just realise the magical grit recycling forever ain't mch better than the notion of using a milling cutter forever, yes works good for a while, but as things dull you get significantly reduced performance. Hence why im in - use the minimum amount of grit and change oftern camp, Grits pretty cheap unlike electric and time!
