Once, early on I had a rig set up for getting high quality CDR's from LP's. I had no power filters of any kind. When playing back the CDR, there was noise in the sound field of the CDR. I could almost hear a faint radio station. I had a "noise sniffer" and it confirmed a very noisy AC line. I bought a Monster Power conditioner. I put it in the chain and did the dub again. On playback, the noise was gone.
Another scenario; I had an Adcom power amp (GF5800, I think). Everytime I powered it up in the winter, the tiny amount of static that I discharged on my audio rack, would cause my Adcoms' overload light to come on. It would go back out BUT I didn't want this happening. I bought a PS Audio power filter. After putting it in the chain, the issue with the Adcom was gone! The results don't always have to have a very audible benefit to justify having one. Cheers. Joe