No need to be very useful at all. Just convenient. We got remote controls for our media devices, to save us getting off our butts. Now its a way of life - channel surfing.
An internet-connected coffee pot or dishwasher is hard to appreciate now. But what if they alerted and called a service guy if they failed? That would be handy. We'd come to hate the non-connected device that didn't appear on our 'household service dashboard' app. It'd be like having a Victrola in the house.