If i am not mistaken the adjustable cam pulley allows adjustment of valve timing as mentioned above.

At low engine speed you would want the intake valve to open slightly before the exhaust valve close totally to take advantage of the vacuum caused by the exiting exhaust to pull more air and fuel in.

At high speed the intake should open AFTER the exhaust closes because if they overlap, the incoming air and fuel will go straight out the exhaust because it's moving at much higher speed causing loss of power.

So you can adjust the valve timings to suit what you are looking for. BUT you ask 'then isn't that only one setting?' Exactly! so welcome to the age of VVTi,i-VTEC,VANOS,CVVT,DVVT,MIVEC, variable valve timing. Variable valve timing now allows the engine to adjust itself the best conditions for every engine speed.