In order to connect to a host you may use this parameter. Every-time you want to get or change any settings on a local/remote device you need to connect to it.
You could use the localhost address (127.0.0.1) to control a device connected to the same computer where you are running the Displax service or the IP address of a computer on the same network followed by a device parameter.
For example if you want to list the devices on localhost you may type:
displaxservice -a 127.0.0.1 -l
If you want to list the devices connected on a computer on the same network:
displaxservice -a 192.168.1.50 -l