There is an enormous difference between drawing a face and drawing a head. The former refers to a portion of the latter as if it were somehow completely unrelated.
In my early years of drawing I was preoccupied with drawing faces and not heads. I wanted all of the features to be well drawn (nose, mouth, and for goodness sakes the EYES)! The problem with that approach however is that it treats the whole three dimensional form and proportion of the head as an ancillary concern and that is a critical error. I think there is a tendency for beginning draftsman to do the same. If a person is not careful, it can become a detrimental lifelong habit.
I drew these heads quickly while observing and sketching at the mall. Notice that the features of the heads are only loosely suggested. I think these sketches are a good example of the strength of observing, thinking about and drawing the head in it's entirety. The head itself has character. It is more than just a shell upon which to draw an interesting face. The head has shape, gesture, planes, anatomy, proportions and deviations from the norm that all add up to make it completely unique and full of life.
Draw a well constructed, interesting head with character and you will have a dynamic drawing which strengthens your draftsmanship and far exceeds successfully drawing a face alone.