As ground bounce is an issue that GTL circuits are susceptible to we'll use it as an example of how changing GTL Reference voltages provides a work-around. The faster an output device switches the higher the transient currents become that are seen by the input of the receiver. As a result, the device ground rises (bounces) in relation to the board ground. The ground bounce is generated during the low-to-high signal transition.
The following oscilloscope screenshot shows an output signal in the top trace and a receiver input at device ground potential in the bottom trace. The ground bounce is easily seen as the output signal switches from high to low. If this bounce is severe enough that it crosses VIL(max) the GTL circuit may see this as logic high and the output will switch accordingly. A bounce can also be seen when the driver is switching from low to high. This is the result of minor switching current within the device and is so small as to be of no consequence.