Writing it beforehand - Why do you want to discard efficiently?

Source: http://blog.jpmahjong.net/read.php/503.htm

This is the first article to address intermediate players of Japanese Mahjong. After reviewing feedback from readers, the author will first start with tile efficiency.

I believe that the readers here have all played Cantonese or Taiwanese mahjong. Compared to them, Japanese mahjong requires a higher requirement of tile efficiency. So once everyone has learned the rules, they'll have to spend some time learning tile efficiency, in order to improve their results. As I explain why tile efficiency is so important in Japanese mahjong, I'll also explain the special characteristics of Japanese mahjong's system.

Japanese mahjong compares position, not points
Beginners in Japanese mahjong has to remember this, Japanese mahjong compares position, not points. Japanese mahjong uses a tonpuusen or a hanchan as a calculation unit. Your results will be equivalent to every unit's average position. In a tonpuusen, just because you win a hand doesn't mean you'll be first, but if you can't even win a single hand, you definitely won't win. Cantonese mahjong allows you to make a big hand every time, because a single big win is equivalent to 10 small wins. However, this playing style won't work in Japanese mahjong. If you can't win a single hand, you'll lose badly.

The importance of closed hands
If you look closely at the yakus of Japanese mahjong, you'll realize the importance of closed hands in Japanese mahjong. You can declare riichi as long as your hand is closed, not only does it fulfill the requirement of having at least one yaku but also allows you to flip open the ura-dora. Japanese mahjong also has a lot of yakus that require closed hands, or having reduced value if your hand is open.

If you want a closed hand, then you'll need to rely on the tiles that you draw. Because the tiles that you can rely on is lesser, good tile efficiency is about increasing the probability of improving your hand. The importance of tile efficiency is much higher than in Taiwanese mahjong.

Japanese mahjong's scoring system
Japanese mahjong's scoring system is also unique. For a 1-4 han hand, every extra han is equivalent to double the score, but 5 han and above is another story. For example, a 5 han hand is mangan. Add an extra han and it'll be haneman, but the score will only increase by 50%. Adding an extra han to a 6 han hand is useless, as 7 han is also a haneman.

A 8 han hand's scoring in Cantonese mahjong is 8 times of a 5 han hand, while it's only 2 times in Japanese mahjong. Hence in Japanese mahjong, few will go for a big hand, since the efficiency is too low. In a game with 3 aka dora, everyone has an average of close to 2 doras. This becomes clearer when you are getting 3-4 han just by winning.

Because there's a lot of dora, winning with a 3-4 han hand is not hard, thus winning with a closed hand is more advantageous than waiting for a big hand. If you want to increase your winning rate, a good efficiency is required.

Now that the useless stuff is over, the next article will get to the main point.