I've never really understood the goal of having an amp... I get that it amplify the sound but... explain to me!
Well, it also would depend on the headphones you would be using. If you're amping the Apple earbuds then it's not going to do anything really because they aren't good in the first place. But with good headphones (I use Westone 4Rs as my main set, which is an extreme example), an amp will not only amplify the sound, but will also improve areas where the headphones lack.
For example, the Westone 4R uses 4 drivers, 2 woofers, 1 mid, and 1 high. The two woofers provide very fast, detailed and accurate bass since they are smaller, but they don't have as much bass depth and punch as a dynamic driver, or a triple driver headphone. So with the amp, it helps bring out the bass and adjusts the output of certain areas of the music. It also helps tone the mids without killing any of the highs, but I won't get too far into that part
It just makes listening to music just that more enjoyable. Especially with lossless files.