Tile efficiency is a process of hand development, where a player seeks to make maximized use of either draws and/or discards to attain or even complete the hand as fast as possible. It rests on the limited number of draws, discards, and even hands, that players can use to win or even try to win. Tile sources come from the opening hand, wall draws, and other players. It is up to the player to make the best decision on tile draws and discards.
Unlike Poker or many other card games, the hand value is not a determinant towards winning. Instead, it is a matter of who develops a winning hand first. Of course, for defensive purposes, a player may outright disregard tile efficiency and abandon the hand instead.
Taatsu 「塔子」 are numbered tile pairs in need of one more in order to complete a sequence. Examples such as 1-2 needing a 3; 3-5 needing a 4; and 6-7 needing either a 5 or 8. When developing a hand, it is often good practice to maintain these tile pairs in order to increase the chances of completing sequences and thus completing the hand.
When building hands, yaku are certainly considered as they are a criteria for valid hands as well as added value to the hand. So, almost always, players have yaku in mind.
In other cases, players may end up simply having tenpai in mind, especially as the hand nears the later discards. This is of particular concern for the current dealer, who may have an interest in retaining the position and repeat the hand.
When developing the hand, tiles take on different shapes, especially when taatsu are involved. The hand will lean in search of particular tiles, by which some many no longer be available. They may either be discarded, have one as the dora indicator, or be in a player's tile call. Any tile, whose whereabouts are unknown, are considered to be live tiles.