I can see the desire to charge and listen to something, granted, you'll be stuck in one spot as your power cable needs to be plugged into an outlet.
Perhaps office workers at a desk job would be the majority of people with this desire?
With that being said, who actually does this and in what situation?
As someone who needs to recharge his phone 2-3 times every single work day (because let's face it, all iPhones are designed for light to no use for it to reach the "all day battery" status) I really, REALLY hate having to go through the trouble of needing to switch cables. Then again, I already gave up and stopped using iPhone to listen to music. I've broken two of those godawful adapters and I am never going to buy lightning headphones. Makes zero sense to buy crap that only works with a single device. Considering I'm already charging a device in all of the 4 ports of my USB charger I'm not really looking forward to having to charge headphones, too.
Luckily the dedicated player option was a much better solution than using iPhone to listen to music. I can rely on my quality (corded) cans and I probably survive with only two full recharges per day. I _NEED_ to keep my phone in charger at the office for it to last long enough when I need to go to a customer.
My work mates are pretty much all in a similar situation. But hey, it's only ~100 of us, must be an isolated incident.
I wish they'd make an iphone model for those who actually use it for work.