Most of us know how important it is to represent the skull before we draw the face so that our character has a realistic shape. Drawing the circle also helps place the hair correctly on the head and besides, how many of us used to draw the face and then realise it looks flat. I know I did. So yes, I really cannot stress the importance of the simple circle when drawing the face. You can also draw it before drawing the actual eye and then build your way up from there. Your eye will have much more volume, I can promise you that and the same technique can be applied when drawing anime.