Another common use for bus drivers on a DAC is to isolate the DAC inputs from the bus so that the data from the other MCU activity on the input will not show up as noise on the output. Often used on higher resolution devices, along with having a separate dedicated digital supply for the bus driver, just to get the noise figure closer to the thermal noise of the DAC and reference. Adds an extra gate delay, and needs a separate enable pin to drive it from the address decode logic, but gives a stable data drive to the DAC latches.