The what, when and why of wireframes
James Kelway posts a summary of wireframes - what they are, different types, and why and when to use them.
One of the why's:
To help designers and developers
They allow development teams to start developing functional aspects highlighted in the wireframe templates before visual design begins. They render the structure of the site from a concept into a skeleton of the final design, ready for the surface design.
Kelway also provides a nifty diagram of the wireframe's journey through a development cycle:

The above image and many others have also been posted on Flickr - IA Diagrams set.

