Depending on the particular DAP there may be physical size and storage advantages. Furthermore most ‘premium’ smartphones do not come with a headphone jack meaning that the audio experience using a decent pair of IEMs will be an improvement on listening to music on a smartphone via a pair of wireless headphones/earbuds.
P.S.
I’ve yet to come across a pair of wireless earbuds that are as comfortable or sound as good as my favorite pair of IEMs.
Depending on the particular DAP there may be physical size and storage advantages. Furthermore most ‘premium’ smartphones do not come with a headphone jack meaning that the audio experience using a decent pair of IEMs will be an improvement on listening to music on a smartphone via a pair of wireless headphones/earbuds.
P.S. I’ve yet to come across a pair of wireless earbuds that are as comfortable or sound as good as my favorite pair of IEMs.