Advantages and Disadvantages of Calling
One of the areas where the difference between strong and weak players shows up most clearly is calling.
You often see players who fail to call hands that should be called,
and also players who call hands that really should be completed closed.
So if you want to relearn calling properly, the first step is to confirm its advantages and disadvantages.
◆ Advantage 1: You reach tenpai faster
Calling will definitely make your hand reach tenpai faster, and it will also make your win come sooner.
That is a very big advantage,
because by winning quickly, you can also crush another player’s chance hand.
◆ Advantage 2: You can build hands that are hard to finish closed
Hands like Honitsu and Chanta are hard to complete as menzen hands,
but once you start calling, they are much less painful.
Flush hands are basically built through calling in the first place;
this is not the mahjong manga world where menzen honitsu hands appear one after another.
◆ Advantage 3: You can fix weak points such as penchan
Dora
For example, suppose two copies of 
are already visible in the pond.
If your upper player now discards another , you should chi it without hesitation.
If you cling to menzen in a spot like this, your chance of winning becomes extremely thin.
If you are not consciously aware that “two 3m are already out,”
you may pass the 3m and miss your chance to win.
◆ Advantage 4: You can create a new meld or improve your wait
Dora
This hand is already a mangan tenpai, but the wait is terrible: a shanpon on and the dora tile.
In this kind of position, if your lower player discards , you should chi immediately.
You can see that the wait becomes much better.
This is exactly the kind of technique you absolutely need to learn.
◆ Other advantages
You can also erase ippatsu,
and you can skip, disrupt, or shift other players’ tsumo order.
◆ Disadvantage 1: Your hand becomes cheaper
Sanshoku and Honitsu lose value when opened,
and Iipeikou and Pinfu disappear entirely.
And of course, you can no longer riichi.
Calling also means giving up ippatsu and ura-dora,
so once you open your hand, a clear drop in scoring power is often unavoidable.
This is the biggest drawback of calling.
This is an extreme example, but nobody would call with a hand like this, right?
(Except in a last-hand situation where any win gives you first place.)
You cannot win mahjong just by repeatedly taking cheap wins.
If you complete the hand closed, at least you still have riichi.
Even if it is only a no-yaku hand, once you riichi, there is always the possibility of mangan.
Hold back that urge to call,
and try focusing more on keeping your hand closed.
◆ Disadvantage 2: Your hand becomes easier to read
Beginners do not need to worry about this yet.
You can skip it for now.
◆ Disadvantage 3: Your defense becomes weaker
If you have already made three calls and are down to only four tiles in your hand,
what happens when another player riichis?
There is almost no way to defend yourself.
If you are still menzen, at least you can still turn and defend.
Of course, if you always full-push no matter what, maybe you do not care anyway.
But in mahjong, there are more hands you fail to win than hands you actually win.
That means you will spend more time on the defensive side than on the winning side.
So naturally, I think you should always be playing with “what if someone riichis?” somewhere in mind.
◆ Disadvantage 4: Your hand gets fixed, and your yaku routes become limited
Dora
For example, suppose someone discards Chun with this hand.
Should you pon it?
I would not call.
Because if you pon Chun here, the hand is worth only 1000 points.
This hand should discard the two Chun and go for Men-Tan-Pin.
It still keeps the possibility of Iipeikou and Sanshoku, and it may also use the dora.
Even if the second Chun appears, I still would not call.
That was the detailed version, but in simple terms:
Advantage of calling .... speed goes up ↑
Disadvantages of calling .... scoring power goes down ↓, defense goes down ↓
That is a good enough way to understand it.
So with these advantages and disadvantages in mind,
let us continue thinking about when you should call and when you should not.
Original Japanese page: http://beginners.biz/naki/naki01.html