No, it's not. Not when you can trivially have access to your entire collection and don't have to predict what you will be in the mood for. Not when you can avoid having to periodically swap out what subset of music you have on your phone at any given time. Not when you can leave more room for other content.
Of course copying all that data to the phone in the first place is kind of daffy. That's what cloud storage is for. Compressed formats still make sense for cheaper, faster streaming though.