Low-Bandwidth X (LBX) attempts to recognize that in this day and age, not everyone will be a fast LAN hop or two away from the system that they are running their applications on.
The X protocol can generate an extraordinary amount of traffic, especially for simple-seeming things such as creating new windows. As anyone who has tried to use X over a dial-in modem at 28.8 or even higher can attest, creating new X windows can involve an excruciating wait.
LBX is fundamentally a compression and caching scheme designed to minimize the amount of X traffic generated between two systems.