Like others here, I use mine as a sort of “kiosk” for smart home stuff by using Guided Access to lock it to a single app. If you have a Mac you could also put it into real single-app mode via Apple Configurator policies, but it’s more time-consuming to set up and if the app stops working there’s no way to fix it short of restarting the entire iPad (whereas you can end Guided Access, restart the app, and start Guided Access again).