This thread shows how to do it in Poser, and what it does.

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2280990

And here is a tutorial. Although it isn't using Poser, it demonstrates what this sort of thing is for.

http://www.cgarchitect.com/resources/tutorials/misc/tutorial2.asp

Basically, it's a very fast way to lift some 2D object from a photo and quickly make a 3D version. The 3D version will not look right if you move move or rotate it more than about 20 to 30 degrees in any direction, but it can work in many cases. The tutorial shows the creation of a whole building, but that's not the most common use case.

Imagine you have a need to make a trash filled alley. You want to quickly make a few cardboard boxes to throw around. Photograph some boxes, position a Poser box in front of the photo, and you can instantly map the photo box onto the 3D box. Then you can move several of these into place in your scene as background stuff, freely moving them and, within some reasonable limits, you can rotate them a bit.

It's a lot less work than taking six photos of a cardboard box and assembling them into the prop's UV map layout.

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