Hmmmm - I know I answered this post, but obviously it never made it to the thread. So sorry. ;-)
There isn't much associated with screening granite or cherrystone over insect screen except for a little dust. I don't bother to collect this, it just falls on the lawn. Turface MVP or Allsport though, are different. What passes through insect screening often gets added to my raised beds. It's ideal as the 'sand' fraction in hypertufa projects, too. You can make some really cool troughs & planters from hypertufa! Finally, if I think I'm going to need a little extra water retention in a particular planting, I'll add the Turface fines to the 5:1:1 mix. FWIW - there would be no advantage in adding them to heavy soils based on peat, compost, coir, or other fine particulates.