While the overlapping grip is the most commonly used style on the PGA Tour, it's interesting to note that many of golf's greatest players favored the interlocking style. Tiger Woods and Rory McIlroy use the interlocking grip, as did the legendary Jack Nicklaus throughout his career. The interlocking grip may have several advantages, depending on your swing style and ability level.
The interlock is a variation to the traditional Vardon grip, in which the right pinky -- for a right-handed golfer -- rests over the left index finger behind the shaft. As with the traditional Vardon grip, the left thumb runs straight down the shaft -- or just right of center -- and the right thumb rests on top of the left. The "V" between the right thumb and forefinger should point fairly close to your right breast pocket.
The most significant advantage to the interlocking grip is the connection it creates between the left and right hand. With an overlapping grip, it's much easier for the hands to separate during the backswing. This separation can force the swing off-plane and cause errant shots. An interlocking grip promotes a strong link between the left and right hand, and forces them to stay connected during all phases of the swing.
According to Ben Hogan, in his book "Five Lessons: The Modern Fundamentals of Golf," the backswing should be initiated by a gentle pull of the middle and ring fingers of the right hand. Although Hogan used an overlapping grip, he suggested hooking the right pinky between index and middle fingers of the left hand to take it out of play. Grasping too firmly with the right pinky, index finger or thumb during the backswing can cause the golfer to "pick up" the club during the backswing. Using an interlocking grip can promote the proper feel of the middle and ring fingers of the right hand.
If nothing else, the interlocking grip allows for consistency in each swing. Because the overlapping grip is prone to separation between each hand, one swing may feel connected while another may not. Keeping the right pinky interlocked allows you to attain the same grip and feel throughout each swing.