Note: RB922UAG: The USB port has independent bus - 1. The other miniPCIe slot closer to SFP slots has independent bus - 2. Depending on USB port type the power reset is done on USB port or miniPCIe slot. This offers a simple way to install the macOS 10.15 beta release onto a test Mac, either on a separate drive or partition.
Advanced Mac users can make a bootable macOS Catalina beta installer drive using a USB flash drive.