For example, when composing a portrait, a photographer needs to consider where the subject is looking -- especially if it is away from the camera. All sorts of visual tension is created depending on how you frame your subject.
You'll often see this rule in action while reading newspapers. For example, if you have a person in the photo looking to the right, then that is where the page designer will try to position the text. If he puts it on the left, the article will seem disassociated from the photo.
Used effectively, it can create an interesting look. Used poorly, it just seems like bad photography.
Exhibit A:
Remarks: WTF???
However, when it comes to advertising I rarely see creative that uses visual tension without being completely intrusive and annoying. The window-shade, roll-down units are probably the worst, followed closely by the floating fly-bys for solicitations to register or take surveys.
So I'm intrigued with this new composition by Apple:
They've occupied both the 728 banner position, as well as the right rail. You've basically got Mac-guy and PC-guy having a conversation that physically (virtually?) flows across the upper-right corner of the content you are reading. Even with the sound off, I am intrigued to hear what they are saying!
Certainly, sustaining the dialog between these characters is a great (and obvious?) campaign-extension from the TV ads, but it's also neat how they're able to get my attention without being intrusive. And somehow I doubt shoving their two heads at opposite ends of a 728 banner would have been as effective.