GoNoles, I think that you are asking how to tell if brass is going to split and when? And if there is any danger in shooting split brass.
If so, here are some thoughts.
The general premise of "shoot till it splits" is the thought that for pistol brass mainly, most of us don't bother tracking how many times the brass has been reloaded, we just keep loading and shooting until the brass starts wearing out. One way that brass wears out is by splitting, another is the primer pockets get loose and another is the impending separation (rifle brass).
As to when, that is the question. Revolver shooters sometimes experience mouth splits soon from repeated working of the mouth from flare, crimp, resize.
Other times it's just luck of the draw.
Most times splits happen on firing, and other times during sizing. Obviously, you should be able to find split brass as you inspect prior to loading. You can actually hear a difference if you have a split piece in a handful of good brass. It makes a different sound. More like a muted thud than a tinkle. You have to try it some time, it's an interesting effect.
As to the other when - what brass? I've had FC 223 brass that neck split on the second firing. Known once fired, resized, reloaded, fired and around 15-20 out of 100 split. In another case, a buddy had some 6.5x55 practice rounds (wooden or plastic bullets) and nearly all the cases split on the first firing.
Lastly, we shouldn't shoot obviously split brass, but if we shoot brass and it splits during firing, then that's fine, just scrap that brass.
On rifles, the issue of impending separation is a different animal. Walkalong has a thread on how to detect it.