One use-case is to monitor and notify when a certain appliance either starts or stops. Washer and Dryer machines stopping is a good example. Another use would be for monitoring an emergency sump-pump - if you ever see it power on, then maybe the primary sump-pump has failed. Nice to get a notification.
I recently had a Nest Thermostat fail in a strange way… Its base plate developed an internal short that caused the auxiliary heat strips to turn on and run at 10kW for about 9 hours straight, until I woke up and noticed that the house didn’t ‘feel right’. The temperature on the Nest said with was about 75degF, the Air Conditioning was running full blast, yet the air from the vents was still slightly warm…with an outdoor temperature of about 40 degrees! I knew something was wrong for sure. Having the energy usage data in InfluxDB and being able to visualize it via Grafana showed me a scenario that should not be possible - Auxilairy Heat and AC both running constantly for about 8-9 hours! I yanked the Nest off the wall and disconnected the AUX heat wire. This resolved the issue until I replaced the Nest with an Ecobee thermostat.
I have also caught my teenage son disabling all power savings features on his gaming PC (i.e. MAX Performance ) Being able to visualize the data, it was simple to see the impact to energy usage before and after the change.