If you got a chance to interact with dealers on a daily basis and started asking them how they set gains, you'd be appalled. And most of them can't distinguish if the signal is clipping or if they can hear distortion in the setup. Most of them don't even know how to set XO points and once music starts playing, they set a "V" EQ and send the client out of the shop.
The DMM method has almost reduced the complaints of dealers that the setup is sounding harsh by around 80%. We cater to around 250 dealers all across India for Zapco, so I'd anyday advocate this method over letting untrained, clueless dealers/clients from destroying equipment setting gains the wrong way.
While people like you, Karan, Piyush and many other ICE gurus here have the ability to set gains by ear or by using an O-Scope or by RTA, majority of the public doesn't understand any of this and this method helps that crowd from blowing things up.
Using this method sets a few things in order:
1. The HU volume now becomes 75% from the 25-30% the clueless dealers would set it at earlier.
2. Gains on the amp are nearly 50-60% lesser now than what they'd set it at earlier, which means the amplifiers run cooler, don't break down due to thermal shutdown, speakers are safer because they don't get a clipped signal.
Obviously, these are all our personal observations from having to deal with a ton of people on a daily basis who don't understand how to set gains and have been doing it wrong nearly their entire lives. Hoping that they'll set it the right way by "using their ears'' is akin to letting a monkey loose with a loaded gun amidst a huge crowd of homo sapiens. Our warranty claims on amplifier sales have almost come down by 90% now and the fact that companies like Sonicelectronics still run that article on their website so that even uninformed, newbies who pick up equipment from them online don't end up blowing stuff.