I also think it's useful for people who tend to listen at lower volume levels on headphones (particularly sensitive headphones). For example, at 50mv I tested that with a 0dbFS sine wave at 1khz I would be hitting around 85 decibels with my HyperX Cloud II (a more sensitive pair of headphones I own). Since this is peak levels, music will likely sit lower in RMS as the dynamic range is higher. But plenty of people do like to listen to music at lower volume levels than 85db, so this metric can more accurately show how clean the signal is at the levels they realistically listen to music at.