FSA and Tournaments both are obvious materials sinks to offset the fact that your city will be producing goods over time in an unlimited fashion.
Even so, I found it just a little startling when one of our senior members in ValHalla plunked down 70,000 silk to help clear a crossroads. It just shows me how far I have yet to go. (I'm only in the middle of Chapter III so I really did have a clue as to that, but it was still startling.)