Delayed Auto Shift
Delayed Auto Shift or DAS is a mechanism similar to how key repeat works on a keyboard. “Repeat delay” (Windows) or “Delay Until Repeat” (macOS) controls how long you must hold a key before it begins to repeat.
Without repeating keys, pressing and holding a key down will just fire once and do nothing until it is released and pressed again.
Without a repeat delay, pressing a key down will immediately start to repeat, causing many unwanted key presses and typos.
DAS, and key repeat delay solve this problem. A key is pressed and held, firing once, then after a short delay will repeat firing until released.
As a user interface, this has become second nature. Most people might not even think about how it works.
In Tetris, someone decided this function should be called DAS.
Auto Repeat Rate
ARR is the how fast the repeat function is done. This is typically configurable for a keyboard in the system settings. Some Tetris games also feature this customization, though it is more frequently found in fan made games.
ARR in some games is quite slow. Infamously NES Tetris has an ARR of 6 frames per cell, meaning it takes 6 frames to move one cell when repeating. During high speed play it becomes difficult to move pieces to either side of the playfield, which is why hyper tappers are so successful.
Some games can have ARR set to 0 frames per cell, in other words, once repeat kicks in, the piece shoots to the wall instantly. I'm not aware of any official game which features this. It is very abrupt and somewhat confusing if you don't understand what is happening. With very fast ARR, players can move pieces to the column they want without having to wait for the delay between repeats. 40L records are usually attempted with this setting in unofficial games.
1 frame per cell is the best of both worlds. It's fast enough that the game feels good to play, yet it still allows you to skill stop, something not needed in 40L sprints. Other benefits compared to slower values are the ability to execute auto-synchros with more ease.
Values in between 1 and 6 will make skill stopping easier, and anything slower than 6 is frustrating to play.
NES Tetris not only has a slow auto repeat rate, and slow repeat delay (or DAS), it also has no lock delay. No lock delay means as soon as a piece touches the stack of pieces, it will lock into place. When the stack is high enough, moving a piece to the edge of the playfield takes more time than for the piece to fall and lock onto the high stack. Once that happens the game is pretty much unrecoverable. Mastering DAS has been vital for expert-play at these higher levels, and required for maxout scores. DAS can only go so far though, and with levels beyond a certain point are unplayable even with good DAS.
Hyper Tappers like Thor, Koryan, and Joseph, can avoid this literal pitfall and move pieces faster by completely circumventing the repeat delay (DAS) and not engaging the slow auto repeat rate. By holding the controller differently and “vibrating” their thumbs, they are able to achieve faster movement of the piece. Playing these higher levels becomes sustainable, and more survivable than simply using DAS techniques.
They can stack higher, with lower risk, and that gives them the competitive edge.