Options docost an airline money (its sometimes worked into the purchase price for the firm orders) - the price of an option usually secures advance delivery positions and the price of an aircraft and an airline must excercise the option by a date certain (ie, convert the option into a firm order), or pass on the option, thereby losing the money invested in the option. In real life, airlines and the manufacturers work together, and frequently, options are extended, rolled over, applied or cancelled in connection with a new order, etc. If AIRLINE X ordered 25 737s from Boeing, with a further 25 options, and then AIRLINE X determined that it did not need or want the 25 optioned 737s, Boeing would come to some type of arrangement with the carrier either to strech out the deliveries or convert the 25 737 options to a firm order for 8 777s so that AIRLINE X could begin its new long-haul services. If Boeing was unaccommodating to the customer, you can be sure that AIRLINE X would start up its long haul services with A333s.
Other concepts are rolling options (when airlines can pick and chose additional delivery dates later on in the contract), reservations for delivery positions, and the like.