As usual I am late to the conversation..... Is this the open source RockBox operating system that is used for portable MP3 players?
If it is I have only done a defrag after lots of erasing and before addition of individual songs. Can't say that I really noticed much difference to be honest. BTW, my MP3 is an old Archos hard disk device running RockBox operating system. I figured the defrag would sorta gather the pieces and stick them somewhat together, but who knows for sure.