Interactive Markers Bridge: What is its purpose and how it works?

I am referring to the following documentation page:

In the code snippet provided in the section, an InteractiveMarkersBridge node is used, with the two following connections:
  "source": "websight/WebsightServer/interactive_markers",
  "target": "interactive_markers_bridge/InteractiveMarkersBridge/request"
  "source": "interactive_markers_bridge/InteractiveMarkersBridge/reply",
  "target": "websight/WebsightServer/interactive_markers_reply"

However, in the same page, I can read:

There is a minimal working example for the interactive markers in apps/samples/interactive_markers

When I look at this example, I noticed that neither the InteractiveMarkersBridge node, nor the edges are used. The example is 100% working, so it is not clear to me what is the purpose of the InteractiveMarkersBridge node. Can you clarify?

Additionally, when I try to use the InteractiveMarkersBridge node as shown in the documentation, I get sometimes the following error, as soon as I try to move the marker in sight:
PANIC engine/alice/components/PoseTree.cpp@84: Cannot set the transformation xxxxxx. Thus, I am not using it anymore, but I am still curious about what is its purpose…