Simple answer, battery.
Let me guess - lossless collection?For the same reason that I have many different iPods and use them all. My iPod Classic can hold my entire 103GB collection, I use my Nano for audiobooks and my old iPod Photo because if there isn't artwork, it uses the whole display to show the title.
I actually rarely use my iPhone for music anymore even though it's a 64GB. On my 32GB 3GS, I don't even have music on it anymore and may do the same to the 4S. I've never had a reason to want an iPod Touch however.
What do you mean what's the point? So you have an iPhone, yippee, good for you.
Not my experience, listening to locally-stored music on my iphone's music app affects very little the battery on my ip4 - music is one of the least battery-intensive things you can do especailly for a long time. Streaming music on the other hand is much worse, forget about videos or games. Otherwise some valid points-it's just that the convenience of having one device overrules all the other issues.Simple answer, battery.
I am often out and about all day with no means of charging my phone up. I can't listen to music on my phone or the battery will not last. An iPod solves that.
There are other benefits as well. At work I can put my iPod in my dock to listen to music but still have my phone to hand when I need it. I can also store far more music on my iPod than I would be able to on my phone is it isn't full of other things.
Of course playing music won't use up the battery by itself, but you also need to use the phone for it's primary purposes.Not my experience, listening to locally-stored music on my iphone's music app affects very little the battery on my ip4 - music is one of the least battery-intensive things you can do especailly for a long time.