Remember the time Apple gave the iPhone a new connector and you had to buy a dongle to use all your old accessories? It's happening again. But worse. Apple's new Macbook has a do-everything USB type-3 connector. That's good! But there's only one on the entire laptop. That's bad!
The idea here is that wireless is the future. Wireless mice, wireless displays, wireless internet via a hot-spot on your phone. Who needs ports?!?! In the future, hopefully no one, but if your ageing gear is still more cable focused, well....
Want to charge your laptop and plug in your iPhone at the same time? Buy a dongle. Want to plug your laptop into an external monitor without relying on battery life? Buy a dongle. Want to do more thing than once at any given time ever? Buy a dongle. It costs £65 and comes in two flavours: USB Type-3, HDMI and regular USB or the exact same thing but with VGA instead of HDMI.
Buy the dongle. Love the dongle. Dongle is life. Dongle is 65 pounds.