From what I'm understanding, so far: it's a 3rd layer bitcoin application on the lightning network, that allows low friction, private, offline/online payments. There's the third party involved as the "mint", but you can also be the mint and then you're the third party. If it's necessary for bitcoin? No. Although it is another interesting option that may or may not catch on. Lightning network definitely did catch on as a 2nd layer (it's also potential third party involved, but you don't see many sceptics anymore).