I’ve got a few on my phone:

• one for playing a sound when my phone is charged
• another for starting my Streaks timer when certain reading apps are opened, so that I can track how long I read every day across apps automatically
• when my Sleep schedule begins (when I’m going to bed), I automatically change the screen colour to grey to help prevent being distracted. When I wake up, it turns that off.
• I have one HomePod, and I don’t use it much, but it has a temperature sensor and when that goes over 25C I get a notification so I know to turn on the AC