The main use case I've heard is video transfers. If you shoot videos longer than a few seconds on your iPhone, you will appreciate a way to get them off of you

The main use case I've heard is video transfers. If you shoot videos longer than a few seconds on your iPhone, you will appreciate a way to get them off of your phone at a non-glacial pace. For professionals shooting significant amounts of video, this is more than a convenience feature. Once your device's internal storage fills up with video, which does not take long at 4K60, now your "camera" is a paperweight until you can dump that footage. Obviously, only a very small percentage of people are using their phones this way. But I think Apple really values that market.