Here is a link to a article/transcribe of a video I linked to in another thread.
http://snazzylabs.com/article/iphone-7-lightning-headphones/
Here is a long quote from that.
"People buy headphones but don’t drive them to their full potential because they’re underpowered.
The biggest part is that new headphones will start to come out with a Lightning cable that has a DAC and amp already integrated. Philips already took a shot at this, but the first really good headphone is the Audeze Sine which will be released in April. I got to listen to them at CES and I was blown away. These headphones will ship with two cables—one regular one for all of your other devices, and one Lightning cable with a DAC and amp combo. With the regular 3.5mm headphone cable, they sounded nice plugged into an iPad (which, remember, used the iPad’s internal DAC and amp); however,
when I changed the cable to the Lightning cable, which had it’s own DAC and amp, I was blown away. The headphones sounded like they were plugged into a really good amp. Because they were. The one built into the cable! Headphones act and sound differently with different amplification types and different DACs. Who better than the headphone manufacturer to design and pair a perfect DAC and amp right from the factory!
People buy headphones but don’t drive them to their full potential because they’re underpowered. Imagine if Audio-Technica sold a $30-50 removable cable designed to work with ATH-M50 you already own that had a DAC and amp designed specifically to work and to power those headphone to their full potential. That’s incredible. That takes portable fidelity to a whole new level. And, if Apple changes to Lightning, new, compatible headphones will popup within weeks. People seem to forget that Apple is an extremely powerful company and if you want to make a successful product, you’ll conform to what Apple makes you do. If we quickly backtrack to 2007, there was the infamous recessed headphone jack on the original iPhone. Apple did it for pure ascetics and there was outrage because there were essentially no headphones at that time which had a jack that fit into that skinny little port. Sure, people like Belkin and Griffin took advantage of selling $15-20 adapters for while, but the entire market moved toward this thinner headphone jack as a result. Today, in 2016, you almost can’t buy a headphone with a fat connector. So, we can naturally disregard the notion that headphone manufacturers won’t start to offer Lightning cables for their headphones, because they will. And if you don’t want to buy new headphones, fine, use an adapter that sounds better than the iPhone 6S. And if you don’t want cables, Bluetooth works great, and will only get better."
Removing the jack will improve audio quality for everyone, as it moves you off the 3.5mm port and into the better Lightning port. There will likely even be a audio quality difference between current 3.5mm free EarPods and the free Lightning EarPods that will probably be bundled. It doesn't matter if "you can use Lightning already with the 3.5mm still present in the phone". Not everyone will take advantage of that, moving people off the 3.5mm gives everyone the advantage of having higher quality through Lightning. A few headphone companies have already started offering Lightning or even headphones with swappable chords (one for 3.5mm and one for Lightning) It's been said (and there are articles on it) many other headphone manufacturers are already working offering Lightning. Don't forget Apple also owns a "popular" headphone brand. Which can be a huge help in the transition period.
Other things to consider. Take a pair of 3.5mm headphones and place the plug on the front face down where you would plug in. Notice how the plug ends right where the bezel ends? That is not a coincidence. It is because the 3.5mm jack is in the way, forcing the bezel to be that specific height. The screen physically can't be moved down, shrinking the bezel because the jack. (Look at ifixit teardowns, the 3.5mm module blocks any possibility of shrinking the bezel and getting the screen closer to the edge of the phone.)
Thinking even further down the road, Apple already has patents on removing the home button and it being integrated right into the screen. Which can further provide a smaller bezel. That can't be done with a 3.5mm taking up the space. Removing it now is a "chess" move today for a move later on. And at the same time provides better audio.