The practical downside is that it might make equations go slightly wonky, rather than completely wonky if a non-number is returned. For example, say if a zero

The practical downside is that it might make equations go slightly wonky, rather than completely wonky if a non-number is returned. For example, say if a zero divide happens with normalized values. Meaning the immediate result is only off by one at most. Odds of catching that are probably low. Meanwhile, a NaN will infect all numbers that come into contact with it, bubbling up faster... Under this system, programs are easier to debug if they use bigger numbers... That property does not seem like a win to me. If I attempt to open a file, but an access fault occurs, I'd rather be told the fault and given a chance to recover than receive an empty file.