Good. But then some strange configuration comes up, and you've suddenly got two drywall edges that you need to connect...with nothing but empty air underneath.
The temptation is to just lay down the tape and mud it over and pray for the best, but this joint runs for several feet. This ad hoc fix will not work because the crack will develop between those two sheets far faster than you can ever imagine. We're not talking years; it's more like months.
Fix: Avoid "hanging joints" in the first place by thinking ahead and planning. Since studs run vertically, make sure that you're avoiding horizontal drywall joints as much as possible. Hanging joints are acceptable when installing long sheets horizontally, and the length of the "hang" is sixteen inches (remember, studs are usually sixteen inches on center).
But more than that, and you've got trouble. If you're dealing with lengthy spaces, then tack in a stud or even a 1"x1" to provide some type of support.
