Why do we need truly holistic simulation? Because people's behaviour and comfort does not depend exclusively on a single physical domain (e.g., lighting, air quality, acoustic, thermal, etc.) but on all of them together, and more. Hence, if we want to nudge people towards a more sustainable behaviour or if we want to design buildings they find comfortable, we need to perform truly holistic analyses.
In simple terms, SIMPLE Simulation Tools is an attempt to bring the qualitative insights of Buildings for People into Simulation... but you can use it however you want.