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 Times Mirror Magazines, Inc., used under license by GolfServ Online, Inc. Instructional information provided by Golf Magazine.