Wall mount light switches that have a neat light indicator that turns on when the switch is in "off" position are quite common. The purpose is to make finding the switch in the dark easier.
Looks like outlets would benefit from this too if they had a light indicator that is permanently on. This way it's easier to find the outlet behind the table and also it's immediately clear if there's a power outage (or the breaker has tripped).
Yet I've never seen an outlet with a light indicator.
What are they not in use?