Turning on a light when motion is dectected is basic, basic stuff. Whatever stability issue there could be with ST (I have it, and they're overstated IMO) using IFFT would bring even more latency issues.
IMO if you just want that functionnality a HA setup is overkill. Just buy a LED nighlight with motion or light sensor for 10$ and you're done. For my bathroom I went simple but high-class and replaced an outlet with one like this.