In chapter 4 of Serway⁷, you will find that the optimal launch angle of a projectile is 45°. However, this condition only occurs when other forces are negligible, more specifically the lift forces. The forces that govern a golf shot are the drag force, the lift force, and the force of gravity.

In the literature read, there seems to be disagreement in arriving at the optimal launch angle for a drive. These discrepancies arise since some feel that the drag and lift forces vary linearly with velocity (Erlichson¹), while others feel that the drag and lift forces vary directly with the square of the velocity (MacDonald⁴).

Accepted equations for the drag and lift force in physics are:
F_d = 0.5pAC_dV²
F_L = 0.5pC_LV²
where p is density of air, A is cross sectional area, C_d is drag coefficient, and C_L is the lift coefficient.

All agree that the optimum launch angle is much less than the 45° of a vacuum. Values range from 13° to 20°. The path of the golf ball follows a linear path for 2/3 of it's flight, then takes on a parabolic path for the remaining 1/3 of flight. This can be explained by the fact that the lifting force acts in a direction perpendicular to its path, countering the effects of gravity, and as it slows the lifting force decreases and the ball falls to the earth.

"http://www.hillendale.com/htm/clubfit2htm"

Golf drivers are designed with approximate 10° loft angles. At this angle, the ball will run further once it lands. If you were to add a couple degrees the ball may carry further, but the net distance would be less.