Perhaps the single biggest reason that anyone thinks of a power conditioner is for protection of their equipment. Certainly the home theater customer has typically invested thousand of dollars in their AV systems, and a surge in voltage or a lightning strike could spell disaster. The idea here is to draw enough current to trip the house circuit breaker, or the power conditioner's fuse, should a surge of high voltage be encountered, thus protecting your equipment. Beware of cheaply made power conditioners or protection devices, as their MOV elements are typically one time use only, leaving your system unprotected after a surge. Our company's products, for instance, use a huge MOV that is over rated for its output, thus allowing multiple surges to take place without any damage to our product or your equipment.
Lightning strikes are a different story.
In areas where lightning strikes are common, the savvy home owner may want to invest in an old fashioned grounded lightning rod on their roof. The second most important reason for the inclusion of a power conditioner is the elimination of noise from the AC line. Noise is created by radio stations, television stations, cellular phones, and all manner of radiating electronics prevalent in our modern society. Their reduction or elimination can have a positive benefit to our audio video system's performance. Most power conditioners use a filter to reduce these noises.