In the Berlin Defence, why is 4.0-0 prefered to 4.Nc3? In the Berlin Defence, why is 4.0-0 preferred to 4.Nc3, as then White can transition into the four knights?
In a comment that ought to be an answer, @Ellie said: “The transposition from the Berlin Defense (1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4...) to the Four Knights Game (Spanish variation 4.Nc3) is a perfectly valid one, but the four knights game is known to be a quite dry opening for white, as in there are various easily equalizing lines for black, starting from the Rubinstein 4...Nd4 (see Kramnik games). Instead 4.O-O is the more critical line (one that offers more hanging fruits...) alongside the 4.d3 line which is known as an anti-Berlin approach.”