if you are talking about the auto/power switch beside the auto gear lever(not the O/D button), the manual says:
'Sport/Power Mode:
For powerful acceleration in sporty driving or driving up long slopes. Push the automatic transmission mode switch to the SPORT/POWER position. The S/POWER insicator light will come on. The transmission shifts into SPORT/POWER driving pattern. As the transmission may always shift in higher engine revolution (higher vehicle speed), you can obtain powerful acceleration in passing or climbing.'
ie. engine rev higher before gear shift...