Unfortunately, a lot of appliances have jumped on the IoT bandwagon, but have missed the wood for the trees. They all want you to use their own proprietary app to control it. This cripples the biggest advantage of IoT, synergies.

A tumble dryer that you can turn on and off from an app is fairly useless. A tumble dryer that can sync its load with the other appliances, and the current solar panel output is a different story. Even with simpler setups there are synergies. Having a light pulse when the washing is done could be extremely useful to some people. Particularly if the appliance is in another part of the house.

As for smart locks... The less said about them, the better. Unfortunately, the "S" in IoT stands for security. That's fine for a lightbulb etc, but not for a critical door lock. It's frustrating. I would love a decent smart, well made, door lock, with a viable open protocol. They just don't exist yet.

As for why a smart lock would be good? Dynamic access control. With a normal lock, if you give someone a key, they have full access, whenever. They can also copy your key, and so taking it back isn't always reliable. A smart lock lets you authorise and de-authorise people on the fly. E.g. it works normally for you, but your mother in law's login (keycard, dongle, app, fingerprint etc) sets off a warning on your phone. You might also want to let a delivery driver open the door, while watching them through a camera. Your package is now secured, and even the driver can't get back to it.

I have a Yale front door lock tied in to Home Assistant through Zigbee. It's completely controlled locally.

I own a bed and breakfast. The day a guest arrives, I have homemade apps that get the last 4 digits of their phone numbers and program them into the lock. The day they leave those numbers are deleted from the lock. The lock also runs on schedules. It locks at 10pm and unlocks at 7:30am, unless we have no guests where it just always stays locked.

It's so so nice. It's also pretty secure.