The extra power is for those peaks or "transients" as far as I know. Take for instance Audeze headphones. Most of them want anywhere from 1W-4W "continuous" power, but support up to 15W "peak/max" power. So in order to really unlock those headphones you'd want something that can deliver at least 15W even though you're only going to be using 1W-4W usually. LCD-3 This is especially true if you're using EQ (you will hear clipping if you try to EQ and don't have the power to support it, or just if your headphones can't handle it, whichever comes first).