It's enticing for many players to take a powerful cut at the ball. However, in trying to build a solid base for a big swing, it's common for the golfer to widen his or her stance until the feet are spread too far apart -- wider than shoulder-width. A wider stance may feel powerful, but it actually restricts the proper weight shift and lower-body coil.
Your stance should be wide enough to supply a solid foundation, but narrow enough to allow lower-body movement. The happy medium is when the feet are about shoulder-width apart. From this stance, your hips should be able to turn freely and your weight should move smoothly from foot to foot without any upper-body sway.

Proper stance width also helps regulate swing speed so you don't lose
control of the clubhead: You can swing as hard as you want so long as you keep
your balance, which is largely a function of stance. If you can't maintain
balance with your feet spread properly, it's a signal that you're swinging too
hard. Rather than spreading your feet to accommodate a fast motion, throttle
down with the upper body. You won't lose power by keeping your stance narrow
because what you sacrifice in arm power will be made up for by an active lower
body.
Width Varies from Club to Club

The shoulder-width rule actually is a little too simple. In fact, your feet
should be a different distance apart for each club. Just inside shoulder-width
is correct for short irons, with the stance widening as the clubs get longer;
with the driver, the feet should be just outside shoulder-width.
Private Lessons 1999 Times Mirror Magazines, Inc., used under license by GolfServ Online, Inc. Instructional information provided by Golf Magazine.