There’s an old saying in photography: know the rules so you know when to break them.
A compositional rule of thumb in portraiture is not to let the nose break the cheek line. If it’s hanging off in space, it tends to make it look much larger and not very flattering.
In this image of Jessica taken a few years ago – and one which is still part of my portfolio – you’ll notice that her nose does in fact extend past her cheek:
However, it’s not hanging off into space but rather backed by her hair. This is why it works – where this rule – can be broken. And in fact, the fact that it is backed, together with the downward angle of her pose, minimizes its apparent size and lends some shape to her face, which might be lost again due to that pose.
The only other time, however, that I break this rule is in a profile shot (a shot where the far eye is not visible – only the lashes). The reason it works in either of these two cases (the shot above and the profile) is that the nose becomes part of the shape of the face. In other poses where it does break the plane of the cheek, the nose is running counter to or “fighting” the shape of the face – you have facial symmetry and then the nose which breaks it. This is why it appears odd and unflattering.
Knowing the rule(s) actually aids you in composition. They’re there for a reason. Knowing when to break them can do the same – if done sparingly and in situations that allow you to.