Sometimes you need to have a connection between far systems, e.g. like in the following picture:
You might want to automatically control supply pumps depending on the water level in a far water tower or reservoir.
With the WebHMI and Level2 connectivity options it is done with ease:
Option 1 Is preffered due to the nature of the MQTT protcol which saves traffice for communication while Modbus TCP will create constant polling process.