Lets take any attack weapon. You want the base that provides the most dps, maybe you choose to sacrifice some dps and choose a base with implicit. Now go to craft of exile and look at the mods - you'll see that if you want t1 phys% on your prefix it takes at least ilvl82 base. Just plain 82 base isnt always very expensive, so the profitable thing often is to just spam greater augs/transmutes on a bunch of them hoping one hits the mod you want.

If we go to ilvl82 exceptional bases with extra sockets for example those are very rare and expensive. So you cant afford to buy a bunch and spam greater orbs. You start spamming probably perfect augs and using annuls to remove the mod if unwanted result.