What is the function of the XBee / USB switch on an XBee shield?
In case someone does ask the same question in the future, this is the explanation for the USB/XBee switch functionality on the XBee Pro Shield V3 
The switch serves to connect/disconnect the XBee Pro shield v3 to the Hardware TX-&gt;1 &amp; RX&lt;-0 Lines of the Arduino. Moving the switch to the USB side, allows you to disconnect the XBee Pro shield v3 from the hardware serial lines and upload code to your Arduino. If the switch is on the XBee side, this allows your XBee Pro shield v3 to use the TX-&gt;1 and RX&lt;-0 lines of the Arduino and if you want to upload code to your Arduino, you would have to remove the shield otherwise it would result in an error trying to upload code.