How often do you find this doesn't quite work as it should?
The problem is that "clerical errors" are maybe 98% of all the errors present in a program if you spent at least some time on design. And even though it usually takes -seconds- to remove most of them, most persistent may lead you to rip hair off your head because you're unable to find them, and later rip hair off your head from shame, after you found them. And because of sheer amount of them popping up, the chances to face hard to fix clerical error are about as high as hard to fix design error. So a good investment in anti-clerical error counter-measures is about as valuable as investment in really good design.