Thanks for the tag. I’ll see if I can keep this simple. 
Before 2018
Up until about 2018, Wi-Fi just wasn’t a very good choice for home automation devices like light switches and sensors. There are the router issues that @nathancu mentioned. It’s a power-hungry protocol, using about 10 times more power than Z wave or Zigbee, which is why battery powered Wi-Fi sensors generally only lasted two or three months as opposed to a year or more for similar Zigbee devices. And there were some very real security questions.
Apple Chimes in
But then… Apple put a lot of research into making Wi-Fi work much better for home automation, probably not coincidentally right around the same time that multiple manufacturers were working on significantly improving battery life. So we started seeing video doorbells and cameras that could be battery operated and run on Wi-Fi and at least get two or three months of battery life. We started seeing a few battery operated sensors. And Apple’s HomeKit significantly beefed up both security and local operations for Wi-Fi devices. That was impressive.
So by early 2020 you could get a HomeKit-based system with Wi-Fi and Bluetooth devices where everything runs locally except the voice assistant and security and privacy are really good. Even the power usage improved somewhat.
2020 Project CHIP and Matter
And then…Apple said, “ you know what, we’re going to share some of our security and privacy technology with (what is now called) the Communication Standards Alliance and we can all work together to come up with a new standard that will work with Wi-Fi and thread and eventually other IP-based protocols so all these devices can talk easily and securely to each other.“ And Matter was (eventually) born. And it may indeed eventually change the whole home automation marketplace.
Apple is all in. Google and Amazon are partners. Samsung has announced that smartthings will support matter.
So…If you want to use Wi-Fi as the basis for your home automation system, you should first check to make sure that your Internet provider allows for unlimited Wi-Fi connections. (Quite a few do, but only if you have their high end plans). You should second check to see how many connections your Wi-Fi router will support, it will be somewhere between 32 and 255.
You should think hard about how many total devices you’re going to need in your home, and whether any of those can be zigbee or thread instead of Wi-Fi.
And if you can be patient, you should wait about a year to see what’s going to happen with matter.
IF YOU CAN’T WAIT
If you can’t wait and you want to use Wi-Fi switches, I would use Meross or another brand that has HomeKit compatibility because those are likely to have the first matter compatibility as well for some technical reasons. (For one thing, they already meet the security standards requirement.)
Or… if you are in the US, You could get Lutron Caseta switches. We don’t know for sure yet whether they will work with matter, but they do work with HomeKit and they do work with smartthings, and they do address pretty much all of the concerns about Wi-Fi for light switches. They don’t use Wi-Fi, they use their own proprietary protocol. It’s really fast, it’s really well engineered, and it only takes one router slot for the whole system and that’s for the smartbridge that you use to integrate with other things. (Lutron IS A member of the group that’s developing Matter, but we don’t yet have any of the details of what they intend to do with it.)
I use Lutron Caseta switches in my own home and am very happy with them.
I also use quite a few Meross Wi-Fi devices, but not as light switches.
I’m not opposed to anybody who wants to use Z wave or Zigbee switches and wants to go ahead with those right now: both are solid technologies and with both you have some good smartthings options.
BUT IF YOU CAN…
So… This whole area changed dramatically just a few months ago with the introduction of matter.
And it’s going to be a little while before we know exactly how smartthings is going to fit into this picture. It could be a major player, in fact it could be the major android player, but we just don’t know that for sure yet.
Usually I tell people not to wait until announced-but-not-yet-delivered technologies are here, but I think this is one of those exceptional times. If you can afford to wait, now is a good time to wait.
But I definitely wouldn’t be getting any Wi-Fi switches right now unless they were already HomeKit compatible or unless they were sonoff. And Sonoff only if that specific model can be flashed to run locally with smart things and doesn’t need a cloud.
I would stay away from anything else which is fairly generic WiFi which needs a cloud until the whole matter situation is worked out.
Just my own opinion, of course.