Heel leads aren't just a pernickity point like Craig banging on about sticking out thumbs though. If you don't get your heel leads right then the movement of your body won't be right, and in particular you won't get the rise and fall needed in certain ballroom dances. In Jay's tango apparently the lack of heel leads was a symptom of insufficiently bent knees which is vital for tango posture.
Huge caveat here - not an actual ballroom dancer myself so this is the stuff I've picked up over the SCD viewing years. But it makes sense - go on, have a go running round your living room with heel leads and see what it does to your head position.