Imagine you are working at a computer all day. At the end of the day, you pull your tablet out of the dock and head for home. It switches from wifi/ethernet to 4g for the ride home them wifi again once you get home. You get an email that requires attention beyond the capability of an email response, so you drop your tablet into a dock in your home office and proceed to solve the problem. In the morning you head to the airport with your tablet in tow. You keep in touch with the office as you travel to your destination. When you arrive at the hotel, you drop your tablet into the hotel's docking station and have the use of a full blown computer station. When you arrive at your business meeting, you again plug in your tablet for full computer access.
You cannot do that with a Fire or an iPad. These things have the potentional to be the next amazing paradigm in the evolution of personal computing.