I’ve got into HA because I have a number of devices that don’t talk. I had also investigated an automated system for UPB switches and dimmers. That was called “Home Control Assistant” (HCA). (close to HA, huh?)
That system worked OK for a few years, for what I was able to do. But integrations were few and far between. It could do UPB and Insteon, as well as RF-based X-10 motion detectors. This required one USB-based UPB transceiver, Insteon transceiver, and a X-10 receiver.
I ran it on a NUC-type SFF PC on Win 10.
And it worked. I could program “turn on and off these lights to this brightness when the Christmas schedule is active” and “Turn the outside light to 30% when it’s dark, then to 100% for 5 minutes after the front motion detector is active”. I even had a “vacation” schedule that would turn on random lights starting at random times and for random durations while it was dark.
These all worked OK. But the iOS app was not what I wanted. But it worked to turn on and off the house fan and Christmas lights when I needed. Also, things we take for granted in HA, like looking at a Lovelace card for a lamp to see when it was on or off required looking at log files in HCA.
The big problem was any new integration was at the mercy of their development cycle.
The product also wasn’t cheap. And the modules, switches, and dimmers were all from one company and if that company went under, I’d be screwed.
I even have a heater on my fish pond outside in the winter, and while my Davis Vantage Pro 2 weather station has a useful temp probe and the ability to use alarms, it doesn’t work over the Internet. Just like my alarm - local is good, but remote would be better.
The real straw that broke the camel’s back is when I needed new thermostats, I went from static programmable ones to Honeywell T5s. I could control those through an app. I was having receiver problems with my old garage door opener, so I got a new one, and it worked via MyQ, another app. I also had a Yamaha receiver, which I could use to stream media from my iOS devices…you guessed it, via another app, and I could get the alarm and weather station working with some hardware and more apps, etc.
Of course, HCA wasn’t committed to these particular platforms, so no feature allowed me to work them all with one system.
I decided I was done paying more money each year for basically static features (at least for what I was using - I didn’t care for Alexa or anything), and for my money, I wanted more flexibility.
I am generally the guy that wants everything to be under my control, so I can configure it how I want. When I get a car, I may ask the salesperson “Do you have a radio that tunes FM continuously, not every 200 kHz?” They would say, “But sir, FM station channels are 200 kHz wide, there’s no need to be able to tune, say, 101.25 MHz!” to which I’d say - well, perhaps I have a receive converter that works on some off-channel FM frequency, I can’t use it with this car!" Or, in my case, I wanted a roof-rack for bikes on my MINI, and had to go OEM. (etc.)
With HA I have (or will have after the Holidays) all the above items on HA. I built a temp probe with a Fibraro Implant with a few DS18B20 weatherproof sensors. Now I have the temp of my pond to verify the temp. And I see it on HA. I have thermostats, garage door opener, Hikvision camera integration, automations for motion brighting lights, alerts on iOS, etc.
One thing I do with HA is decide if I can deal with some old tech in HA, or if I need a new piece of kit. If my old alarm with work with with an Ethernet connection, and it works or is supported in HA, then I’ll keep it. It not, I’ll rip it out and get one that you all say works better.
Another thing I try to do is rely on the old way of doing stuff as a backup (or “local control”). Sure, I could control the pond heat by reading the temp in HA and turning on the plug where the heater is. But I currently have a heater controller that’s right at the pond, so all I need to do is monitor the temp for the unlikely event my heaters go bad…of course, I can’t change the temp without opening the box and adjusting the heat controller outside (not fun in the snow), so once I get some more confidence in HA, Zigbee, Zwave, etc. I may go the HA-only route!
Then, when left with a BIG, HUGE “states gui” page, I can decide what I want to create. Do I want my Hue lights to blink red and send me an iOS alert when the pond is hot, cold, or low? (hint…how do you tell if the pond is low? If you suddenly notice the air temp sensor and the water temp sensor are the same temp, and the water temp is not where you programmed the heater, and you set the water sensor X" below acceptable water level!)
So, the TL;DR answer is Home Monitoring is the first thing you achieve with HA. Even if your only automation is to turn on a light once HA starts, you are still needing a trigger, and a trigger is a monitor! 
Then, like me, you decide, “Hey, it seems like there’s a lot of stuff that I could monitor here…how I can use those data?” and you’re off to the Home Automation races!
See you out on the track!
Cheers,
Ambi
P.S. I might add that one reason to control all your stuff first is to decide how well it works in HA and get used to the entities provided by the devices. My switches and dimmer can tell me how many Watts they’re using. So, I could add up all my switches to estimate power usage. But, maybe you’d want to get an IoTaWatt monitor hooked up to your breaker panel to monitor everything?
But what can you do with the data of “how many watts am I using” at a switch, plug, or breaker? Well, if you turn a string of Christmas lights “on” every night, and they measure 30 watts, what does it mean when the wattage does down to 10 watts? Well, you’ll at least need a history of the power over time, in case 10 watts is some transient anomaly.
But it probably means you want an iOS notification that says “Please check Christmas lights, you may have a bad string of lights” or “Your nephew is playing with the lights again!” - whatever it means to you in your situation!
