Why sacrifice the rook? [Title "White to move"]
[FEN "1r3rk1/1p4bp/p2p1q2/2pPn1p1/B1PnRp2/PPN2P1P/2QB2P1/3R2K1 w - - 5 27"]


This is a diagram from the game between Del Rey, Diego and Efimenko, Zahar on the Zalakaros Chess Festival after 26...Nd4. White answered with 27.Rxd4. I don't understand why white needed to sacrifice his rook for the knight in this position.
Well, he has to because there is no other option. The black Knight threatens to capture the white Queen, but also a 'sacrifice' on f3 which will eventually win the white Knight on c3.

[Title "White to move"]
[FEN "1r3rk1/1p4bp/p2p1q2/2pPn1p1/B1PnRp2/PPN2P1P/2QB2P1/3R2K1 w - - 5 27"]

1. Qb2? Ndxf3+ 2. gxf3 Nexf3+ 3. Kg2 Nxd2 4. Qxd2 Qxc3


This might not even be the best variation for Black. In any case, even after the sacrifice, White is still lost.