If you want to carry your whole music library around, a big SD card makes that work. I understand streaming is the trendy thing and I was using Navidrome myself, but I rolled back my plan and switched to SD card for it. I've saved money.

Another use case is for carrying a heap of ROMs. I've also done this until I realised gaming on my phone was uncomfortable and bought a dedicated device.

Having the SD card wasn't a dealbreaker for me when I bought this phone but I do really like having it.