The input buffer amplifiers for the MCP4902/4912/4922 devices provide low offset voltage and low noise. A Configuration bit for each DAC allows the VREF input to bypass the VREF input buffer amplifiers, achieving a Buffered or Unbuffered mode. Buffered mode provides a very high input impedance, with only minor limitations on the input range and frequency response. Unbuffered ( = 0) is the default configuration. Unbuffered mode provides a wide input range (0V to VDD), with a typical input impedance of 165 \$k\Omega \$ with 7 pF.
I'm having trouble understanding what exactly the buffered mode does. Does it prevent noise from damaging the part by preventing voltage values that are inputted which are just under the range from exceeding the range due to noise? Also, the documentation for the python package is a bit unclear; what sort of value should I input? I assume it relates to how much of a buffer I want there to be, but I don't know what the range of values should be.