Greek Gift Challenge #3 Rac1?

lichess.org/practice/intermediate-tactics/greek-gift/s5pLU7Of/BIsgqPgX

I'm trying to understand the importance of the final required move here. Rac1. Would you please help me?

do not let the opponent have a domainant rook

And a dominant rook is one on an open file? So we put ours there before he can?

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.

OK, thanks. And I just put this in the analysis board and it's recommending Qd3 as the next move instead of Rac1.