Seems odd when it's put this way - yet - most humans are approximately 8 heads high. This can be a quick way to check if you've drawn a figure in pencil and want to see whether you need to adjust before inking it in. Sometimes I take a moment and quickly draw some circles off to the side and afterwards, it becomes apparent to me whether I've made a gigantic head or way too long body or something.
Of course -- with character work, you may want to break all the rules of normal figure drawing in order to have a stylistic and expressive result. So always use the 'rules of thumb' with plenty of exceptions, as you see fit ;)))