Voice Control
Amazon was one of the first companies to offer a voice-based product that worked well. While the Echo Dot with Alexa can do a whole bunch of things on its own (especially if you have an Amazon Prime account), like play music, tell jokes, read Audible books and read the news, it's when you pair it with a hub and other smart home products that it really becomes a useful and foundational tool within your home.
Our favorite use for it is to control lighting in a home. Especially if you are a visitor in an unfamiliar space, acquainting yourself with the various light switches around the house can take time and can be frustrating when you just want to relax. By using simple commands like "downstairs on" or "bedroom 30%" a guest can intuitively control the room from anywhere, without a lot of fiddling.
And of course it also works out great when you're already in bed and realize you forgot to turn the downstairs lights off, or forgot to lock the door!