The dot is obviously not a necessity. That said, it's a fun, handy, inexpensive gadget to have on the kitchen counter. If I'm in the middle of making meatballs or something I can just say, "Alexa, play Eric Johnson music", and seconds later EJ is playing. Don't have to stop what I'm doing, wash my hands, grab my phone, etc. Or, while following a recipe, "Alexa, how many tsblespoons are in a half cup?", or whatever. It's not going to change your life, just a little added convenience. If you have a good wifi signal it's handy, practical, and fun by the pool for calling out music requests.
And as already mentioned, ordering things on the fly is a great feature. "Alexa, order cat food".
It's also fun just asking it random questions, such as, "Alexa, who's the greatest QB of all time?"
Not going to change your world, but you shouldn't be expecting it to for $40.