A little bit of karma tonight....
My wife and I were out running errands and realized we forgot to leave a hall light on for our dog. So that would have been a nice time to be able to do that remotely. He's probably the world's most spoiled dog.
For me, i've been using a program called homeseer for years, now i'm able to add devices from that to homekit using a program called homebridge.
Most of my automation is handled by homeseer, as scripting in homekit is a little lacking.
I mainly use homekit as a "front end" for controlling things. I also have several lighting scenes stored in homekit.
For me, leaving a light on for the cat is automated.
I have a virtual device, that gets automatically turned off/on when i leave or enter my home location.
If that device is off (meaning i'm gone) and it's nighttime, i have it turn on a light.
Also if I'm gone for more than an hour, no matter the time, It will set one of my sonos speakers to NPR, so it's not so quiet for him.
When i get home (combo of my "home" device above, and a door sensor on the front door) It turns on some lights, and plays music. (day and night time have different lighting looks)
I have under cabinet LED lighting in the kitchen, as well as a motion sensor. If the kitchen is dark, and the motion sensor trips, it will bring up the cabinets to a glow, enough to see to refill a drink or put a dish in the sink.
I'd leave it at a glow all the time, but my apartment is small, and the kitchen is open to the living room, and the light spill over.
Siri is helpful here too, since i'll go in and start washing dishes or whatever, and realize i'm still in "dim" mode once i've started, so i can ask her to turn on the lights, and not have to go hit the switch with soapy hands.
I've got an eve button by the bed, i can hit that and turn all the lights off, or turn on just enough light to see to get to the bathroom in the night.
It's nice to be able to say "siri goodnight" as you crawl into bed and have all the lights go out, the ceiling fan turn on, music stop playing, the tv turn off, and my shades close.
Or to be leaving in the morning, and say "hey siri I'm leaving" and have the house turn itself off.
If you're tech savvy, (think if you're the one asking for or being asked by your friends for tech help)
take a look at homebridge, There is a learning curve, but it's mostly configuration to get it working. as people have written plugins for most "smart" devices. I've got my couple year old LG TV, non-homekit camera, and my smart vacuum all working in homekit.
I don't have any nest gear, but i believe there are plugins for all of your devices, so you can add them to homekit.