I believe they ingrain the "feel" of a lagged full-speed swing without swing at the full speed, which allows you to better beware of the rhythm, physics and geometry of the action.
__________________ Yani Tseng, Go! Go! Go! Yani Tseng Did It Again! YOU load and sustain the "LAG", during which the "LAW" releases it, ideally beyond impact.
"Sustain (Yang/陽) the lag (Yin/陰)" is "the unification of Ying and Yang" (陰陽合一).
The "LAW" creates the "effect", which is the "motion" or "feel", with the "cause", which is the "intent" or "command".
"Lag" is the secret of golf, passion is the secret of life.
Think as a golfer, execute like a robot.
Rotate, twist, spin, turn. Bend the shaft.