Assuming the delay/cancellation is the fault of the airline not until either the flight is cancelled or you would miss a connection. That's assuming you're not starting from your "home airport. Also, in the event of a missed connection the gate agent may tell you to fly to the connecting airport and get hotel/food vouchers there, never a good idea. If your flight is massively delayed you may be given the opportunity to rebook the next day without fee/refare but hotel and food would be your responsibility.