The fianchetto is a fundamental strategic concept used in many modern openings, including the King's Indian Defense, Grünfeld Defense, Catalan Opening, and Réti Opening. By placing the bishop on g2 or b2, it controls the long diagonal and provides both attacking potential and defensive solidity.
A fianchettoed bishop on g2, for example, controls the a8-h1 diagonal and often acts as a powerful defender of the kingside while also pressuring the center and queenside. This dual function makes the fianchetto a flexible choice that works well in many different types of positions.
The main strategic consideration with a fianchetto is that trading the fianchettoed bishop often weakens the squares around the king, particularly if the pawns in front of the king have advanced. For this reason, players often try to preserve their fianchettoed bishop and opponents look for opportunities to exchange it. The dark squares around a king that has lost its fianchettoed light-squared bishop (or vice versa) can become chronic weaknesses.