I ran across the attached video by Eric Cogorno with Travis Salzman for which I posted in another thread, but I think it's worth a closer look because I followed-up by doing the drills.
The video is not about the golf swing, it's about how to minimize tension which allows the lower body to move "earlier" to start the downswing. Many folks activate their upper body and arms to start the downswing for which the arms out-race their lower body to the ball because the arms move much faster than the lower body.
The drill in the video is very fun because the goal is to hit a 1/2 distance shot with a full, yet very loose swing. When doing the practice drill I discovered how tense I was before I started the drill. As I hit balls I found the need to get "looser and looser" in increments. It took 30 or so shots to finally get relaxed enough to hit an 80 yard full-swing 8 iron (believe me, it's NOT easy to do). The "miss" was to hit the ball 100 or more yards, so it was like reverse psychology that forced me to relax. As the range session continued, I found it easy to ramp up speed to hit farther, but then I'd go back to 80 yard shots. It's actually very easy to hit the ball WAY "too far" as Travis says in the video. While long shots are not the goal of the drill, it was eye-opening to feel how effortless it can be to hit a much longer shot without "trying".
On the course (where tension is the highest) I employed the same logic with the driver. I only focused on feeling as relaxed as possible to allow my lower body to move earlier. My goal was not to hit long drives. My goal was to feel very relaxed with a balanced finish. Oddly enough, in some cases I hit some of the longest drives I've hit in decades. I used the same approach for my irons and the impact "sound" was different, like a crisper/snappier sound. My thought was to move my lower body earlier, and earlier, and earlier during practice swings because the "1st and 2nd earlier" practice swings were likely still not early enough.
Once I felt the tension free swing, the "tension swings" were quite obvious. Plus, it was VERY easy for the tension swing to pop up, so not all shots were great, but at least I knew why. For me, I picture Fred Couples swing in terms of how effortless and smooth he looks when he swings any club. Then when I had a 145 yard 8 iron shot, I'd take practice swings like I only wanted to hit a 100 yards, then step up and swing because my body knows it needs to ramp up the speed, but I didn't want my brain to "try" to ramp up the speed using my arms/shoulders.
There is no doubt tension is a killer for power. It’s funny, myself and a good buddy of mine used to be professional fighters. We have discussed this at length. When fighting a big difference between real fighters and “tough guys” who don’t know how to hit hard simply tighten up and use muscular effort to build power. Experienced, good fighters, throw punches really relaxed. In fact in fighting often you just want to get the hands moving and then things sync up and power comes on with no effort.
That applies to golf very well. Golf isn’t a game of static positions. It’s a movement that requires things to sync up for effortless power.