You are also just wasting fast storage--often a register--tracking and checking this stuff (at least for any type for which there isn't a natural invalid value,

You are also just wasting fast storage--often a register--tracking and checking this stuff (at least for any type for which there isn't a natural invalid value, such as a null pointer); multiple return points is going to do the same thing, but worse, as you will need to hand the second return point to the called function but will no longer be able to reuse invalid return values.