Assuming you do not want to reverse engineer it then the only use is for some emulators that support it; when making an emulator you have to write code to mimic the BIOS functions but if the BIOS already exists and your emulator is good enough then you can dodge having to write an alternative BIOS or emulate the functions contained within it.
This being said most GBA emulators across all consoles I know of emulate the BIOS well enough to play games and then some, it is more for those that require "flawless" emulation (some coders need it). These days it probably has a negligible effect but there was a speed boost of sorts for some emulators once upon a time.
Team Cosby included the GBA BIOS from a *GBA* console in their
This GBA BIOS comes from a *DS* console (Black EUR USG-001, doesn't
really matter). There's nothing special with this dump, just 1 byte
different from the TS2/Cosby dump, probably just to account for the
system jump, as suggested by an aquatic friend of mine.
it'd be nice if someone could use this to create a .nds emu file that holds lots of gba games. kinda like the gba NES emus do, copy a ton of NES games to create one .gba file that holds all of those games.
@Canonbeat234 yeah it is for collectors, GBA emulator authors and the few who want to use it with an emulator (unnecessary and in the case of the GBA it has been for some time).
Back on topic we have had the GBA BIOS as well as the SDK for using it for years (and tools to dump both this and the DS version for years too) and as people have mentioned this is no different in any way that matters.
This is mildly useful simply because we know it works. There are so many incorrectly dumped GBA BIOS files on the web, and getting this specifically labeled one is a surefire way of making sure you get a good one.