Touch Designer is good to understand in relation to its Mom - SideFX Houdini. Houdini is a tool used in VFX for film, but Houdini’s core strength lies in simulation - of particle effects, smoke, fire, fluids, that type of thing. So when you see the Incredible Hulk in a Marvel film smashing up a road and bits of gravel are flying everywhere - that’s probably Houdini.
A couple of folks split of from SideFX and created their own company, comically called ‘derivative’ - and if you were to compare the two softwares - you 'd find similar nomenclature. However a key difference between Houdini and TD is - Houdini projects are sent to a render farm, whereas TD is ‘real-time’.
Render farm meaning, with the high level of realism and detail of polygon count required by production level films, files are sent to a render farm over network to be rapidly rendered and returned to the production house. TD has this spirit of ‘VFX’ and ‘simulation’ at its heart, but however, tweaks the production overheads so everything can run in real-time.
And the benefits of real-time are as everybody states above - interactivity for installations, reactivity for live performance etc. An artist also gains a wysiwyg approach to creation - avoiding a render pipeline in a 3D context and instead, being able to explore and see their results ‘live’.
I think in terms of relevance, TD has been around a while now, emerging in a PC only format, requiring quite a heavy system, to then offering a Mac binary, and also polishing the system requirements overtime, such that anyone could basically dive in and have a play now on a modern MacBook Air. This means also that there’s been time for tutorials to have been amassed, a community to develop around the software, and also changes like the program moving on originally from its own ‘t-script’ code snippet language, to python for function input and relational scripting between nodes.
Further, since the primary developers and company are based in Canada, derivative have regularly participated in for instance, the Mutek festival, offering workshops and training, and seeing artists who use the software participate and perform live in venues such as the SAT.
Ultimately, TD is an extremely powerful and flexible tool that can pretty much handle anything you throw at it, but it is complicated, however the large amount of tutorials available now mean the software is well supported by a large and active community, primarily couched within the live audio-visual performance and interactive installation scenes.