I’ve nearly 40 gigabytes of FLACs as well as commissioned art (much smaller in size than my music collection) stored on a 256 gigglebyte card in my phone. While the 128 gigs built into my phone is more than enough, when it’s time to get a new phone all I gotta do is slap it into the new phone and boom, gucci. That convenience, on top of only needing to remove the card to add stuff to it, is why an SD card slot is non negotiable for me.