Why is it compulsory to write a game in classic chess tournaments? If the purpose is the validity of the moves, then why not in quick games?
There are several reasons having to write down the moves in standard chess games:
- as a document, proof of the game and result (in some cases but not always the players also have to sign)
- in order to confirm 50-move and 3-fold repetition rules
- in order to count the number of moves which can be relevant for the time control (e.g. sometimes you have say 2 hours for the first 40 moves plus 1 hour for the next 20 moves plus 30 min for the rest)
- to prevent cheating (players changing position of pieces, etc), though this is usually not much of an issue
- for storage (so that you can later analyze your game or sometimes it might even be entered into a database)
With short time controls there is simply no time to write down the moves. Also with some longer time controls, it is sometimes allowed not to write down moves when the remaining time drops below some limit.
Just for information the technicalities on how to record (and how not to) moves are laid out in article 8 of the FIDE laws of chess
The reasons for writing down chess moves are of great importance in classical games with minimum time formats of 1 hour, with 30 secs increment. The uses are:
1) The game is played with longer time, and players try playing the best move on the board. They get more time to think, and the thought process is better displayed.
2) Cheating is obviously prohibited.
3) Chances of silly mistakes happen less during the game as compared to quick/rapid format play.
4) After the game is over, the winning player keeps the game in his own database which inspires him for upcoming matches. The losing player analyses more and learns from his mistakes.
5) During the game it records the 50 move rule, which can leads to a draw.
6) Chess is divided in three phases: Openings, middlegames and endgames. During a longer format, professionals divide this phase according to some precise timings. They make sure they complete the openings in 10 mins, the middlegame in 30 mins, and keep 20 mins for their endgames. After the game is over, they make it a point that they completed the same in the stipulated time . It helps them to think faster with adept in both moves within time.