Quarterback is believed to be the most important position in football, primarily because the QB touches the ball on every offensive snap, and his decisions and level of play often determine his team's success. A taller QB has an easier time both seeing over and throwing over the offensive and defensive linemen, which increases his chance of completing a pass. A study by Bleacher Report showed that, since 1980, ratings of NFL quarterbacks who threw over 350 passes increased with each height increment (with those 6'2" having the highest rating), and completion percentage was lowest for the shortest quarterbacks.
Height can also be an advantage for those who catch the passes. Taller wide receivers and tight ends present a better target for the quarterback, and they have a greater chance of being able to outjump the defensive backs for a pass in traffic. Although the Bleacher Report study showed that smaller NFL receivers had higher per-catch average, their taller counterparts had a higher touchdown percentage. As with other positions in which height is a factor, college coaches are more likely to recruit receivers who have the prototypical size.
Offensive and defensive linemen are generally the largest players on the field, in terms of overall size and body mass. With players at any level of competition, height will often accompany the size and weight needed to play on either side of the line of scrimmage. However, height is more prized in defensive linemen than offensive linemen, as a player on the OL can excel at his position, especially at center, without being overly tall, while a defensive lineman can use his height to bat down balls thrown by the QB, and kicked field goals/PATs, and use his reach to make a greater number of tackles.
Being taller can also be an advantage for those playing in the defensive backfield, though speed is a more important attribute for these positions. As with receivers, height provides an advantage for a cornerback or safety in battling for contested passes. As with defensive linemen --- and linebackers, to a certain extent --- greater size and reach increases the player's ability to make tackles.