Option to abandon

If there were no option available, then going ahead with the investment would mean having to keep it for its entire life, even if the inflows in the future turned out to much less than were originally expected (and had they known about this from the start then maybe they would not have down the investment). Having the option means that if the flows do turn out to be less than expected then they can abandon and not incur the later losses. This is a benefit and the option has a value. It also makes the NPV of the project greater - the knowing that they can abandon if things turn out badly means that the project is more attractive than if they had no choice but to continue with it.