That is the monitor. The smart meter replaces your old meter and gives the energy provider instant, remote access to your supply and energy usage.
The data will be able to tell them when you are using electricity and when you are not.
If you don't pay your bills and the company gets a court order to disconnect your supply it can be done from their offices.
If their is an energy crisis your supply can be disconnected at will (never done without very good reason in extremis). This means that your neighbour who needs a constant supply for a life support machine is never disconnected.
You don't have to use the monitor, you can stick it in a drawer and forget about it but the smart meter will still be in use.
As already stated, the advantages to you are:
no more meter readings
you will know exactly how much you owe the company in real time, in pounds and pence, by looking at the monitor
no more estimated bills