What absolutely must happen during the swing if you want to hit a powerful drive? A strong leg drive? No. A big shoulder turn? No. Lots of arm speed? That's the ticket.
You must swing the arms quickly if you want the club to swing quickly. But many players searching for distance try to add power by turbocharging their leg drive or lunging at the target with the upper body. Too much lateral body action inhibits a free arm swing and throws the clubhead off line, resulting in mishit shots and less rather than more distance.
The body's proper role is as a platform for the generation of arm speed; it exists to react to and support the arms.
Like Throwing a Ball

The golf swing is a lot like throwing a ball.
There's virtually no body movement when you putt, and
there's very little when you make a short toss with a
baseball. There is a great deal of body motion during a
drive, just as there is when a pitcher fires a fastball
to home plate. But the pitcher isn't concerned with how
much body he should put into the pitch. He just wants to
throw the ball hard. His body responds to the effort of
his arm.
The same concept is true of the golf swing. Prove it to yourself around the practice green. Hit a few putts, then chips, then pitches. As you progress, notice that your arm speed increases as the shots get longer. At the same time, your body responds, moving to provide leverage and a greater range of motion for your arms. But the arm swing definitely comes first.
Practice Arm Speed

Your arms can only move so fast, and trying
too hard to develop arm speed will start your body
moving laterally. Determine your maximum arm speed by
experimenting in practice. If you hit your 7-iron 150
yards, slow down your arm speed and use the 7-iron to
hit a ball 90 yards. Increase the speed for the next
shot and try for 120 yards, then hit the third shot 150
yards. Try to swing your arms faster on the fourth,
increasing your speed on subsequent shots until you
either fail to make solid contact or you feel your body
trying to control the club. That's when you'll know
you've reached your limit. Once you know your arm speed
limit, you can go for it every time you want maximum
distance.
Private Lessons 1999 Time4 Media, Inc., used under license by GolfServ Online, Inc. Instructional information provided by Golf Magazine.