Umpires like it when the lines aren't there. At that point it becomes a "judgement" call for the plate ump. Judgement calls can't be argued or appealed. At that point, the ump can let the game be played without having to worry about the feet in addition to; balls, strikes, leaving base early (softball), balks, illegal pitch (softball), catcher obstruction, HBP, batter/coach calling time, foreign objects (stray balls) on the field or any of a number of things that the home plate ump has to watch for in that 3 second period of time between wind up and completion of pitch.