They named the "Feet Together" drill as one of their best ever. It's supposed to provide the player with significantly more distance, while also improving your balance.
I've been incorporating this drill for about a month and a half, and the results have been very illuminating:
Firstly, it's surprising how much distance I've been able to get during this drill. I lose no more than 5-10% of my distance with my irons. This speaks volumes about how UN-important is to sway or slide back and forth during the swing.
Secondly, as a result of working on this drill I've made my stance more narrow. It's now closer to hip-width than shoulder-width. I feel like this is allowing me to load up my right leg during the back swing and move onto a straight left leg during the through swing with a minimum of moving parts.
Thirdly, I've played some of my best golf in decades after starting to include this drill in my range work. This may be a coincidence, but I'm getting too old to believe in a lot of coincidences.
I may be attributing too much of my recent good play to this drill, but the drill really really feels "right".