The Nest thermostat allows me to control the heat remotely.
These two things are great for rental properties. Guests often forget to lock the door, I have records of when guests or maintenance people are coming or going, I can adjust the heat to 55 when nobody is there which saves a lot of money and more importantly I can ensure the heat is not turned off (which could cause frozen pipes) which some guests do for some reason.
Outside of a rental, these things aren't as useful. But I'd still get a programmable keypad (I've been running the Yale touchscreen ones in the mountains for years). It's very handy for friends or maintenance and with a Smartthings hub you can unlock the door remotely and give no code. Or give a code and change it later. I got the one with a key backup just in case but I haven't had the touchscreen fail yet.
I do run the Nest cameras outside and they've been nice to check snow levels, bust the spa maintenance guy for not even showing up, expose a neighbor for stealing firewood and rocks, expose guests who brought an actual bus full of people, expose another guest for filming a movie, and plenty of other things that have been helpful documentation.
It's kind of crazy how far the Nest cams pick up audio and how clear it is. So be cautious of these things because they are constantly recording and it makes it easy to scrub for footage (detects and quick links to voices, dogs barking, people, etc). I only listen to the audio when it's applicable (guests are doing something they shouldn't) but I'd imagine that some homeowners are watching and listening for fun.