Most decent lights have tommyhere so it's not needed. My most important function is dosing. I run 4 pumps on my big tank, that dose every hour or every other hour.
It shuts off my heaters over 78.5 helping to save at least a little energy. It runs a pump 5 minutes per hr inside my ato where i also add some kalk so it keeps it stirred with minimal run time.
It can send alarms to my phone when things go bad.
People use them with leak detectors so they know fast if the floors getting wet.
You can put a camera on it so you can watch while art work.
A better question would be what can't you do with it?