For example, I love being able to switch off the living room's lights, as well as all adjacent rooms' lights, all with two taps on my iPhone, without getting up from the couch. Also nice is turning the lights on/off at certain hours of the day, or when certain triggers occur.
My setup goes: ZWave wall switch <-> (Raspberry Pi) [ZWave hub <-> Mqtt <-> Homebridge] <-> AppleTV (Home Hub) <-> iPhone. Despite all of the moving parts, this has been 100% reliable for me with near-zero latency. It even works well when I'm away from home (albeit with a tenfold increase in latency)
Unfortunately, this setup is not a low/no configuration one, so it's not a solution for the vast majority of people, and is why internet connected IoT (Nest/Alexa/Hue/Insteon) are as popular as they are.
I agree, they work good, but one thing I love most about them is that, if you use IKEA's gateway, they neither require nor provide "the cloud". Everything's local, it's great.
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They can also be turned on and off based on presence, on time of the day, on the fact that you just turned on your TV, etc.
If companies were actually trying to make good products, there would be almost zero drawbacks if we turned all current switches 'smart'. It's just a single bit in the case of switches and lights. The problem is that they want to monetize said bit in addition to the device cost, they want it to talk to a cloud, they want to make it so only their hub can flip the bit, etc. Oh, and they will have unnecessarily complex firmware with security vulnerabilities and that require regular updates. EVEN when most of the logic is in the cloud, which is mind-boggling. And cloud integrations will randomly fail.
I do like the ability to be able to make all things 'smarter'. In particular, I want to be able to collect data from all devices(this all feeds to Home Assistant in my case). When you have all the data, and the ability to remotely control, you start thinking of all the use-cases you can automate.
Today, I can automate when light switches turn on or off, I can have my robo vacuum not run if my 3d printer is running so it won't bump it, I can have reminders to plug in my EV (when the @#%6 Nissan API works properly). I have locally controlled power switches. I can have reminders when laundry is done. If my dishwasher was 'smart' I would be able to control when it runs (as it is, I'm going to jury rig my own solution). Also thinking about automating my garden next (I already have weather forecast information, just need moisture sensors and a pump).
Honestly, we could turn our homes into a Star Trek ship bridge today, if only companies got their act together. I think there will be an 'IoT winter' as consumers get fed up with all the shenanigans.
I built it, so if it breaks I know how to fix it. No chance of the cloud shutting down bricking my devices.
What I do is I think about the massive challenges like climate change and then compare it with what I'm doing. Immediately makes me realise what is worth my time and what is not.
Climate change was just one example. There are some things in my personal life that are just as scary as climate change for me. Immediately snaps me out of wasting my time.
Interestingly, having automated lights and detailed power monitoring has helped me to reduce my average electric consumption by around 20%. Imagine the impact on global warming if everyone reduced their electric consumption by 20%.
Everything was connected to the Home Assistant.
This setup worked 99,9% percent of the time, but occasionally there would be some issues, especially if WiFi or power was down, which would usually mean that devices wouldn't connect to the WiFi, or in some cases ZigBee light bulbs would go into pairing mode (I guess ensuring that I use more expensive Philips Hue bulbs everywhere might solve the latter.)
At some point I just figured out that I want my light switches to work 100% of the time, regardless of the status of network or connected devices (Home Assistant NUC or ZigBee bridges), and that I don't have practical benefits from all the automation and data gathering (Grafana dashboards were nice, but didn't really improve my life in a meaningful way.)