Emulators like Citra or Panda3DS often require this file to properly handle the 3DS's internal encryption and boot sequences.
It contains console-unique data? (Actually, BootROM is identical across all consoles of the same model, but sharing it still exposes Nintendo’s proprietary code.) boot9.bin file
How to study boot-stage firmware responsibly (for researchers and students) Emulators like Citra or Panda3DS often require this
Unlike the Nintendo DS, which utilized a BIOS visible to the user, the 3DS ARM9 BootROM is hidden from the external address space. It is mapped only to the internal address 0xFFFF0000 of the ARM9. boot9.bin file