When to trade pieces

It's usually helpful to trade if you can get ahead but what should you do if a potential trade doesn't gain or lose material? It's usually a mistake to initiate a trade unless you can tell how your position benefits. Good reasons to trade could be to simplify when you're ahead, to remove a well placed opponent's piece or to gain control of an open file.

Both sides are fighting for the only open file. Is trading rooks White's best move?

White increases the tension on the d-file, forcing Black to give up the only open file.