Most amateurs lose unnecessary distance and direction of their drives because of an outside to inside swing path. Simply put they come over the top. The reason for this is because swing path affects not just direction but the angle of attack of the club.
The average golfer can change launch and spin rates with the same clubhead speed and same ball velocity by correcting their swing path, resulting in significant gains. If the average golfer corrects their swing path (the over the top move) by 5 degrees, they can effectively gain 35 extra yards off the tee with a 90mph swing speed.
Most tour players have an inside to outside swing path which creates an upward blow on the ball. The result is a higher ball flight with less spin, creating farther tee shots.