Because the granules are now round, and more uniform in size, they pack or compact well in cartridges, and will do so in your percussion guns. There is no reason to spend the extra money to buy cartridge grade for your flintlocks, as you should not compact the powder in them. You do eliminate the fines you find in FFFg powder, and to some extent, in FFg powder, but I hardly think that is worth the extra cost. you can buy screens for a couple of dollars, and screen your own FFg and FFFg powders to get rid of the fines. You will produce a small quantity of 4Fg powder that you can use for priming powder on those clear sunny days on the range. Then go back to using FFg or FFFG powder for your prime the rest of the time, and when you are in the field.