I'd never heard of doing this, though perhaps that's because my students don't write the type of papers that I'd need to check for this.
Is this new to anyone else, or just to me?
Do the standard plagiarism-checkers such as SafeAssign catch things like this? If they don't, then that's a very good reason to grade papers on the computer (where you'd presumably see a mass of words marked as misspelled) instead of printing them to grade.
So while we're on this subject, what's the most creative way that a student has cheated in one of your courses, or the most blatantly obvious cheating that you've come across, where you want to crack someone upside of the head not for cheating but for presuming that you'd be too stupid to notice the cheating?