The advantage with headphone amps is that it gives oppurtunity for different sonic characteristics without buying the entire reciever.
Ideally, you want to experiment with different kinds amps like at a headphone meet for example. Ideally you want the reciever to have your ideal sound for your speakers. This does not mean that it will have the ideal headphone output.
A great headphone amp like an upscale tube amp will have a better seperation of sound than your average reciever headphone jack. This is something that most average people are not aware of.
If somehow, you love the headphone output of your reciever, that's great. Do not go any further and stick to your reciever. But I think that if you do end up experimenting with dedicated headphone amps, most likely you will find a headphone amp that will be better and more refined than your reciever.
That being said, I love my headphone jack of my Marantz reciever but I know there are headphone amps out there that take the sound even further.
Going further is what head-fi is about!
Remember that brotha!
