74LVC1G125 on the arduino wireless shield?

What does the 74LVC1G125 do on the Arduino wireless sheild? Its just a buffer, but is it really necessary, or is it only necessary if you stack a lot of shields? (ie: collectively increasing input impedance)

Its this shield: http://arduino.cc/en/Main/ArduinoWirelessProtoShield

Answer

The input of the 74LVC1G125 is 5V-tolerant, while the DIN pin of the Xbee module may or may not be. The gate is there to provide level translation, as this is the only signal that flows from the Arduino to the Xbee module.