Gripping down on irons and hybrids to close gaps
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It's something you have to practice. And, it will work better on some clubs than others.
Also, the grip thickness can influence how well the "grip down" works. When I had my wedges regripped this winter, I had the fitter put an extra two wraps of tape under the bottom 4" of the grip (under low hand). This keeps the grip thicker for when you grip down, so you have more even grip pressure. (This is a tip from the GolfWorks crew. It's been around for years, and is becoming popular again).
Along this line, Edel Golf has extra-long grips available for its wedges. This allows you to "grip down" and not have to grip shaft metal. http://edelgolf.com/
For full iron shots, grip down is maybe about a half inch. If I'm between clubs, this allows me to shave a few yards off the longer club. (I only worry about this when I'm swinging well. On bad days, it doesn't help... )
It's more effective trying to shave yards off of partial wedge shots.
Golf tip from last summer: On fairway woods, hold at full length when hitting off a tee, but grip down an inch for better control off the fairway.