I don't have too much "smart home", but I am really tempted by lighting. Being able to dim and change the color temperature of the light depending on the time of day is compelling. Dimming is easy conceptually, but it would mean rewiring large portions of my home. I don't know how I'd manage that with color temperature.
I like 2700K. Wife likes 5000K. Having bulbs that can go back and forth has saved me thousands of dollars by preventing a divorce.
Seriously, though: Controlling multiple bulbs at once is very convenient. Sometimes I sleep downstairs, sometimes upstairs. The lights I want on/off differ in both cases. So a simple routine "Sleep downstairs" and "sleep upstairs" that controls which lights should be on/off is more convenient than getting up and doing them individually. It was mere fun when I programmed it, but once I had it, it was awesome.
Also, having some lights come on at sunset was a real improvement. Gone are the days when I come home during winter to a totally dark house. Granted - you don't need Internet to achieve this.
AC compressors should not operate below 60F outside. Sometimes it's still warm when I sleep but will dip below 60 near dawn. Because of this I can't turn on my window AC all night. I have a smart switch that can handle the wattage of my AC. My next project: Turn it on when I go to sleep, and have it turn off when the outside temperature is below 60F - and turn it back on when it goes above 60F a few hours later.
Philips makes a range of "Warm Glow" LED dumb bulbs that change from ~2700k to 2200k as they dim.
Not nearly the color range (or control ability) you can achieve with something like Hue bulbs, but I've been happy with them for bed side lamps and the like.
You can also put Hue bulbs in and use something like HomeAssistant with the F.lux plugin to control the brightness + color temperature automatically throughout the day. No wall switch-based dimming, but dimmable with a phone.
I'm a big fan of the Hue lights. I've done the IKEA ones, and they are great, but the phone-connected options offer scheduling and automation, if you're into that kind of thing.
I have some led strips installed with a simple remote that allows temp and dim control...I love it and don't think auto changing these with the day would be that big of an improvement than pushing the button a few times until its at where I like it.
