Good point @QTipPoker . I don't see any good reason this move should be included in this training exercise. Rac1 doesn't force anything, and if you play the computer's recommended move for a few moves it doesn't look like there's any decisive gain of material.
Rac1 is a good finesse in the position, though -- white threatens to play Rc7, attacking the vulnerable f7-square. If black blocks the file with ...Nc4, white can play b3 to kick it. If white plays b3 first instead of Rac1, black can play Ba3 and deny the c1-square to the rook.
So white plays Rac1, forcing black to commit the bishop to d6 rather than a3.