It allows faster communication than the "uncachable" setting (the alternative to USWC in the BIOS), as long as the graphics card supports write combining (which most modern cards do), allowing data to be temporarily stored in write combine buffers (WCB) and released in burst mode rather than single bits.
This setting allows for faster data transmission compared to the "uncachable" option, which is a feature of the BIOS. This is achieved by utilizing write combining on modern graphics cards and storing data temporarily in write combine buffers (WCB) before releasing it in bursts.