Some of the advantages are that now headphone devices could have added features like volume boost and noise cancellation and advanced controls that couldn’t have existed until now on headphones due to the fact that these features require power.
The Lightning Connector port could be used for both analogue and digital playback. There are of-course numerous other advantages. Removing the 3.5mm headphone jack will allow more room in future iPhone devices for other things such as a bigger battery or extra modules. On the other side, such a move will have many disadvantages as well. A new standard will most likely upset many of the current Apple fans since they will surely hate not being able to use their already acquired headphones on newer iPhone/iPad devices. As a consequence it is also possible that not so many industry giants will decide to mass produce headphones for the new standard.
This might however be one of the reasons why Apple acquired Beats By Dr Dre. Without any doubt a wide variety of premium headphones will be created by Beats for Apple’s new standard.