what are the two purpose of valve clearance

valve clearance is the clearance between the valve puck and rocker its necessary for 2 reasons, the valve needs to be completely closed during firing and to make complete combustion and the exh needs to be open at the right time to let exhaust escape. improper valve clearance will cause a multitude of issues like misfire or fuel not burning properly

So you're saying there is a pretty clear purpose for clearance of valves?