Power conditioners ARE imporant---however what many consider as a power conditioner really, truly isn't a "conditioner". Personally I would NEVER plug any of my high-tech audio equipment and computers directly into the wall or even a traditional power strip, I don't even do that to my televisions or other high-end electronics. However a $100 box isn't technically a "conditioner" either. There is surge protection and there is SURGE protection, the cheap power strips really don't protect anything when a major surge comes down the pipe. In fact it's been proven that they can cause even worse damage as there is no release for the voltage to let go and, in worst-case scenarios, can catch on-fire. I've seen this demonstrated first-hand and have had (2) clients I know of that have had fires start because of it---one of them even lost his house, that was about 7-years ago I believe.
There are significant advantages to "power conditioners", units such as the Monster Power Pro 2500
even which is a $200 unit. In my new house down here in Buford, GA....I noticed a slight high-pitched noise through my LSR6328 monitors without my computer plugged into the PRo2500. My monitors are through another conditioner, however unlike my past studio where I had multiple circuits--everything is on a single circuit (for now).
As mentioned, VOLTAGE REGULATION is really the best place to start for most home studios and above because it does provide you with a consitant power stream that stays roughly @ 120V. If you're getting too much it pads it down, not enough it pulls more through. The thing to remember is, even if you have a brand new home with brand new wiring--it doesn't matter when it comes to your studio gear. The electric company is providing power to power your house, the lights, etc. But with sensitive audio gear, those little fluctuations allllllll day long every day really can cause problems over time. This is even more important when we start talking live sound. I do a decent amount of large-scale productions, clean power---and I'm talking Regulation of Voltage AND Balanced Power (the good stuff!) are not only needed, they are critical to the sound of the equipment. Yes, clean and stable power matters to your sound quality. There is a great deal of electrical noise in the lines, as that is cleaned out it allows for a more balanced and true power signal to power your gear allowing for higher useage with more efficiency. IT's for the same reason we use high-quality master clocks for converters, to clear out the "jitter" that's in the audio stream. In high-end studios (meaning commercial OR home-studios), this kind of power is critical to get the most out of your gear.
Unfortunately many think that just buying a real power conditioner will fix any kind of electrical issue but it doesn't, unless you are buying the expensive stuff. If you have a hum in your line, it may not always be the answer. Sometimes you do have to look at the line itself, hire an electrician to look at it, possibly new wiring etc. So is a power conditioner always the answer? No, but it's a heck of a lot better than just plugging straight into the wall----but don't buy one without knowing what it is you're buying and why. Just because it racks and you plug into it, doesn't mean it's worth it or the one you should get.