Very useful to have at a glance if the boiler is running without having access to the boiler display.
This is standard in almost all the thermostats.
And show it in the graphs too, particularly for boilers like mine that only have on/off. And not just for the zone that triggered the boiler, just whenever it fired. Maybe a use a color to indicate it was triggered by another zone. I have to check every zone now to see if heat was requested, and then Im still not sure if the boiler was triggered or not.
Im not kidding when I say I mounted an old smartphone to my boiler as webcam and for audio to check activity while testing.