When it gets to that point (between 18-25 firings) if the primer seats and stays in the pocket when shaken I'll shoot it. BANG! If it falls out I retrieve the unspent primer and toss that case. But, I have to say that I almost only shoot Lapua brass, and while I generally cycle 500 cases in rotation (enough for two matches in a row) the pockets are all gona give out within a firing or three. When the first one goes I can accurately guess that about half are going to be no good, and I may as well toss all of them after the next firing rather that get 1/3 of them loaded again, which is now not enough for a single major match.
I expect my cases to last two seasons and eat through two barrels at least. If I'm on my third barrel it's time to buy new brass (which can be as expensive as a barrel).
However, I spend more on bullets than anything, and I go MK, so about $130 for 500.