Worked on this for the first time at a lesson this week. I'm not a short hitter (9i is my 145-150 club), but I've still never understood how some of my buddies can get their 9i out there 160-170, 200 yard 6i's, etc. etc. After being shown that I was making a lateral move forward, and subsequently started working on keeping my head behind the ball at impact, my shots are at new level. I almost instantly gained a club length throughout the bag. Not only that, irons launch WAY higher and thus land much softer with a lot more spin. Driver is still a work in progress with this swing change, but when I catch it's almost 20 yards longer.
Point being, I think this is extremely important. Definitely a game changer.