Projector bulbs
The bulb/lamp in a rear or front projector gets really hot when running. To cool it off and extend the life of the lamp, the TV or projector runs the fan for a few minutes after you turn it off. Unplugging a projector or a power outage will eliminate this cool down stage which could shorten the life of the lamp.
If you have frequent power outages, then a battery backup might be a wise investment. APC and Tripplite have models specifically designed for A/V gear that include surge protection, voltage filtering and regulation, and battery backup.