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.

I’ve enjoyed using it for a room controller for my AV distribution system. one of those perpetually unfinished work in progress projects and money-sinks.

So a few little wall mounted android things running fully kiosk browser, each one with it’s own room control panel using the WallPanel add-on from HACS to get a customisable toolbarless view, card-mod for some custom CSS and a few other tweaks, also node-red running to do some logic, sequencing and handling the REST commands that are a pain to implement directly in HA. Each room panel has control over lighting, climate, TV and Audio. Each room has a TV connected to a 8x8 HDMI2.0 matrix with a selection of Nvidia Shields, TV and Sat tuners and an appleTV, along with a dedicated dashboard with weather, rain radar and camera views. This is all done in lovelace with custom navigation buttons instead of a toolbar in a simple grid layout with minimal options per page.

So when a user taps the media icon in their room, they get a list of available sources for the TV, guest rooms only have one Nvidia shield available (specifically for guest users) and the main bedrooms get their personal one. The shared living areas and theatre have access to any source so any user can pull up their dedicated shield with their content, apps and accounts.

This also means that I can push any video source to any room intelligently, so I can have a party mode that mirrors every screen, or use any form of presence detection to send a doorbell image to the nearest TV, or a surveillance feed, I just haven’t implemented any of that as I dont need to yet.

The only difficulty is remotes, currently I’m using super cheap hacked OneForAll remotes with custom codes and macros, but if someone selects a source on the touch panel they have to select it again on the remote to get control, so mostly people change source with the remote as I have that set up in a macro. I despise using touch devices as a remote control. If I can get a smarter remote solution worked out I’ll do it, it would require a man in the middle to process remote commands from the IR system, recognise the room it is in and the active source in that room and forward on the right commands to the matrix for distribution. possible, but a pain as I’d have to program it from scratch on an arduino or esp32, or more likely one per room.

A two things that will run when the house is unattended.

The vacation mode can do things like turn on more lights than you would have normally, turn on the TV or some music, etc.

In Progress, needs tweaking:
Making sure our AC only turns on when it can efficiently cool the house. Useful when we dip into the 50's for lows while it's 70's+ during the day. Basically switch the thermostat to heat only to avoid the AC coming on.

In the planning stage:
Presence sensing in our bathroom to turn the light on for my dad in the middle of the night. Can't use PIR motion detection as my dad moves very slow these days and actually defeats the PIR sensor in our hallway night light. I'm thinking mmWave is the way to go. Might try presence sensing when someone is on the toilet, turn the fan on, again, because sometimes he forgets.

Just getting started really with automations right now.

I have A LOT of automations. Some of my favorites are:

• Automatically set "house state" (morning, day, evening, night, not home, etc.") based on alarm state, time of day, last movement, etc - this state controls a lot of other automations
• Push message to my phone if outside camera detect a person when house state is "night" or "not home" (using Frigate for object detection)
• Automatically turn off lights at night or when not home. Automatically set lights to right level when home
• Push message when window has been open for more than 20 minutes.
• Push message if windows or doors are open when leaving the house or at night
• Push message with "morning update" and "evening update". Including today's weather, if I should sell some stocks as price has reached threshold, etc.

Basically, I no longer has to remember to turn on of off lights and if I forget something important in the house (such as an open window or turning on the alarm), it reminds me to do so (if it can't do it itself)

I don’t have many, I find home assistant is a tool in search of a need.

• Run the robot vacuum when I leave the house.
• When I arrive home or open the garage door after sunset, turns on the rear porch lights and then turns it off after 15 minutes. (I have a detached garage.)
• Turn on select outdoor lights at sunset.
• Turns off all outdoor lights at sunrise, so if I forget to turn off the lights around my deck they eventually do get turned off.
• I have a button near where I sit in the living room that controls all four lights in the living room.
• I have a button on my dashboard that just turns off all the lights in my house.
• I have a button near my bar that turns on multiple lights and a neon sign. I was intending to add effects and scenes around the bar too so I could press another button and have a show go off.