The same reason people buy shit because Steve Meade uses it and therefore it must be good. The same reason why people feel like they have to buy an amplifier rated for xxx amount of power to "properly" power their subwoofers. The same reason why some people think all mainstream products are crap, such as JL, and everything "underground" that isn't known to the mass is the best stuff ever. So it can detect a lower level of distortion, so what? If your ears can't tell the difference, then why does it matter? Your listening to the music with your ears, not some mic or analyzer that goes "OH shit, 1% thd, negative points negative points." I understand your need to set the gains as high as you can on your monoblock amplifiers because you want it to be as loud as possible for your bass, right? The different in output from having the gain set between these two methods: "right below audible distortion from the ear (gain set by ear)" and "DD-1 with less then 1% distortion" isn't going to be audible. You would have to be off by enough so that the amplifier is making half it's power, thus creating at most, a 3dB difference. Which means you have a lot of headroom to be off, and your ears wouldn't be able to tell the difference. Your just pissing your money away. Or your using it for setting the gain for your front stage amp, well shit that should be easy to hear audible distortion, turn it down to where you can't hear it, and your set. Your acting like all music is 100% distortion free, and any distortion, no matter how small percentage, added to the mix is going to wreck havoc. If your competing, playing constant sine waves, and you want to play it at the highest level possible before excessive clipping, then I guess that's a different story.