Idea of this connector is to have one hole blocked on mother side, yet exist 5V connectors (Chinese love such) that are universal and do not have blocked hole for 5V addressable connector, so nice people plug them into their 12V one. If hole is blocked, people use some force and still do the same, just bending third pin.
Usually 5V strips or fan leds do not survive such 12V thing.
It looks like you're new here. If you want to get involved, click one of these buttons!