At a basic function level, LLTD(Link-Layer Topology Discovery) gives users a graphical representation of their home network topology. In addition to the network map, LLTD offers network device manufacturers a standard way of ensuring that their devices are easily viewed and accessible to their users. Windows Vista enables the Network Map by default when a user is in a location designated as “Home.” However, LLTD and, therefore, the Network Map are both disabled by default in “Work” and “Public” locations.
You will receive a message inside the Network Map (Control Panel -> Network and Sharing Center -> Network Map) if the map is disabled. As long as your network policy (group policy) does not prohibit it, enabling the Network Map on a local machine is simply a matter of enabling the right setting in the local computer policy. “Network mapping is disabled by default on domain networks. Your network administrator can use Group Policy to enable mapping.”
Beyond offering users the convenience of having a visual representation and providing right-click access to information about the devices, the LLTD Responder also plays an important role in responding to, and taking part in, network diagnostics. LLTD helps to make distributed and coordinated network diagnostics possible, and if you are creating home network devices, you should strongly consider implementing an LLTD responder.
(source Link-Layer Topology Discovery Mapper I/O Driver and Responder
And on your second issue, I guess I'm a bit confused as to what you mean by "master browser".