You're leaving the house in the day and returning at an unknown time in the eve. Light comes on at sunset. You're forced on WeMo app to specify a time to switch off. You want this to be bedtime but this is different evert night. But the light switches off at a specified time while you're watching TV. Alternatively, you can cancel the daily sunset On and timed Off but you must now remember to turn this schedule on again the next day.
The uncatered-for use case is someone wanting the light to come on at sunset for security and then to stay on until manual switch off.
This is especially helpful to people who do not have the mobile next to them all the time and who walk over to the socket switch at bedtime.