SBS 2003 R2 SP2 Exchange in Mixed Mode

SBS is a new world for me.  I normally work on the enterprise side. 
Usually 
I begin my installs with Mixed Mode in the Exchange 2003 realm and then 
eventually set it to Native.

I noticed my recent SBS 2003 R2 SP2 install it is in Mixed mode.  Should I

set it to Native?  Is there any benefit?  The network is 90% XP and the
rest 
is Vista B/E.

Thanks