TouchDesigner is more for interactive applications, like reactive Video projections, installation content, where the visuals react in accordance to data collected in real-time (from sensors, game-pads, Kinect devices, or even information from websites). TouchDesigner, like most software geared towards real-time applications, has less processor intensive operators for geometry manipulation and shading (raytracing!) operations, Nevertheless, the amount of flexibility it can achieve with realtime signal processing data manipulation is still very amazing. This is especially easy on interatctive visual designers when it uses node based visual programming and the Python scripting language.
I was recently trying to explain the idea of proceduralism in CG / VFX / Interactive applications to a friend, and I kept thinking back to these couple of Houdini demo videos of how powerful a workflow it is.
These videos were posted by Kim Goossens on his/her YouTube channel. They still amaze me with the power of Houdini to this day.