For me, my favourites are definetely some light automations, namingly

• motion detectors and window sensors (where there aren’t insect nets) turning on and off the lights
• adaptive lighting automations setting brightness and shade based on the time

more than that

• turning down the (usually somewhat loud) music in the bathroom when I open the window to the street
• running the vaccuum when I’m not at home
• heating automations adapting to the weather report, presence, time and user preset

my future idea is to copy a nuki opener with an esp-32.