We deployed about 200 Jabra headsets throughout the enterprise. For highest quality, you really want to use the little dongle. The sales reps will tell you this too, and in our testing, those who pooh-poohed this and used only BT had significantly lower quality (until they flipped to the dongle).
Between my new WfH keyboard (Dell KB700) and my headset research, I had an eye-opening education on this point. The KB700 is 3-device Bluetooth, with one of those devices permanently paired to the included USB dongle. The expectation is the dongle goes to your PC, and the remaining "slots" are for pairing with a smartphone and tablet. It was a head-scratcher to find a Bluetooth device that more-or-less needs its BT dongle, instead of just pairing directly to the computer's internal BT.
After finding the same paradigm with wireless headsets, I found this video, and it made a little more sense.