A typical use for the load output is for a well pump. The well pump will run from the battery as long as the battery is charged. After the sun goes down and the battery starts to run down the load output will turn off and the well pump will stop.
This feature is found on the following Victron MPPT Charge Controllers
Like everything else on these charge controllers the load output can be configured. Its easiest to do with the Bluetooth charge controllers but can be done with them all. Here is an excerpt from the manual:
3.6 The load output
The load out output can be configured with Bluetooth or via VE.Direct.
Alternatively, a jumper can be used to to configure the load output as follows:
No jumper: BatteryLife algorithm
(see manual for more details)
Low voltage load disconnect: 11,1V or 22,2V
Jumper between pin 1 and pin 2:
Automatic load reconnect: 13,1V or 26,2V
Low voltage load disconnect: 11,8V or 23,6V
Jumper between pin 2 and pin 3:
Automatic load reconnect: 14V or 28V
Programming the load output by Bluetooth is even easier, a screenshot is below: