Technical Photography!

Above demonstrates the rule of third. Often the main image is based on the left two thirds leaving the right free for any tag lines or plugs etc... If the main subjects or focal points are located around one of the intersection points (points around the middle box) it makes it more interesting to the eye rather than if the image is placed directly in the centre and it's where they eye is usually instantly drawn to.

Allure magazine uses the main image of Eva to draw attention in from readers. They try to place the focus on her eyes as this is based around two of the intersection points. Although her head is mostly in the centre of the magazine, the turning of the face adds interest. As the main feature they're trying to attract you to is her eyes is allows for them to add their plugs/tag lines down the right third. The mast head is also in the top third which means that it isn't effecting the main focus of her face.