The idea is to ground the equipment powered by continuous low voltage DC – Internet box, telephone with wired handset, ECO DECT phone (often placed on the desktop), various devices on charge, Switch, Hub, fibre optic converter/RJ45…. in short, when the grounding USB cord solution does not allow it (no built-in USB port or metal USB not connected to the device’s metal frame).
Images are better than words, see the following examples :