it all depends how you want to manage security I guess.
we disable it as you may have domain admins who are not dba's, who will get SA access if bultin\administrators is not disabled.
we have a very tight nit security policy where there is only one account which has SA rights across the whole board.
we as DBA's only have limited access with our windows accounts, should we need to do anything admin related we login as the account with SA access.