As per the the voltage regulation in power conditioners, home theater electronics are not sensitive to damage from under voltage. As was mentioned earlier there is already power conditioning in the electronic equipment. They just may not function optimally or perhaps even just shut down from the under voltage. Surges on the other hand are definitely destructive to home theater equipment and need to be addressed accordingly with a whole house surge protector and proper earth ground.
Anything with motors that are operating in your home you have to be careful from under voltage like fans, fridges, freezers, water pumps, sump pumps etc. These appliances can fail from overheating as the motor increases it current as the voltage sags/drops.
The water pump in our home seems most sensitive to under voltage. This was noticed/caused by a problem from our generator that was operating under voltage. Also I have seen this with overhead fans in our washrooms on utility power.
I still like the idea of uninterrupted power supplies to prevent data corruption/loss.
