The goal of this drill is to land on top of an elevated surface without having to arch the body. The gymnast can't arch and twist, which is why the drill is so important.
Open-tuck and layout yurchenkos to progressively elevated mats are good drills. The gymnast can add open-tuck twists to the feet and eventually to the back. Gymnasts should not attempt the second somersault until they can consistently land on their back on an elevated surface.
Practicing yurchenko timers to stacked mats is a useful way to train different vaulting techniques without having to worry about injuries. As the gymnasts get better, they can raise the height to make the drill more challenging.
Yurchenko layouts are commonly used by competitive gymnasts as warm-ups for more difficult yurchenko vaults involving multiple twists. Take a look at these varied yurchenko timers from different video angles.
The straps training is a convenient way to practice and develop reverse hechts timers without burning the hands. At first the gymnasts may practice hecht timers from big swings emphasizing a quick shoulder angle opening and a change from hollow to tight arch body positions before the swings moves under the horizontal.