It is a very powerful tool. Unfortunately, just like many other plugins, it is ignored by the community because of the lack of manuals or tutorials that tell how to use it.
I was talking last year with DesignDevil about a problem an animator may encounter when rendering a walkthrough animation. If the animator decides to use simple planes painted with a tree texture rather than 3D trees, and if the camera moves around these trees, the 2D nature of the trees will show up and break the illusion.
You may say that the animator can use the Look_At tool, to make the trees always facing the camera. It works, as long as the camera does not fly over them... as the trees would bend and pass through the ground !
Here is a trick found by DesignDevil, using trueConstraints plugin.
The idea is to create an object (here a cube) that will be linked both to the tree plane via the Look_At tool, and to the camera via trueConstraints.
We simply keep the tree vertical by keeping the cube location at Z 0 while the camera flies in the air.
