Quite a few years ago I was using Shawn Clement's lessons & concepts on YouTube ... ended up buying the DVD's.
One of his many drills was the "feet together drill", simply placing feet together and swinging rhythmically (letting my arms fall using only gravity) about 1/2 way back and then 1/2 way through as many times as possible without losing balance.
During a round I would do this drill when I wasn't in anyone field of view so as not to distract them, I thought it helped because my usual swing thought was "put a flat spot on the back of the ball", a thought occasionally rewarded but more frequently penalized. I began to wonder how far I could hit it with the "feet together drill".
Through experimentation I found I could hit a 9i almost exactly 90 yds .... repeatedly & with spin which is not my game. I had some luck with 80 yd PW's and 100 yd 8i but the 9i was dependable and repeatable.
As much as I tried to maintain the rhythm I achieved with this drill, I was never able to transfer that feeling to a full swing so I only use it when I can play my 2nd shot to 90 yds & the trusted 9i comes out.