Every monitor with a USB hub and every printer I’ve owned for the last 20 years has had one. It’s used to differentiate USB directionality, for example which side is upstream or the “host device” and which side is meant to plug into the computer.
They’re moot now with USB C which is bidirectional; USB-A male to USB-A male is dangerous and not compliant with the USB specification, so they’d use USB-B on one side.
Every monitor with a USB hub and every printer I’ve owned for the last 20 years has had one. It’s used to differentiate USB directionality, for example which side is upstream or the “host device” and which side is meant to plug into the computer.
They’re moot now with USB C which is bidirectional; USB-A male to USB-A male is dangerous and not compliant with the USB specification, so they’d use USB-B on one side.