Well, this is an interesting question. I assume you are talking about the party that owns the oil (the state or private company, whatever the case may be) as opposed to society as a whole. I will answer from the point of view of the resource owner, please correct me if you meant society.
For a private company, most models show the optimal time to extract as yesterday, meaning that you are worse off each successive day you leave a resource in ground. It comes down to this: Will the oil in the ground appreciate in value at a rate greater than my discount rate? If the answer is no, you want to extract now. For a private company, the answer will probably indeed be no. Why? You have investors who demand a return, and often you have debt or other competing projects to employ valuable capital. You must also consider that the constant appreciation of natural resources is not a forgone conclusion. In fact, many resource economists would argue that the opposite is often true. We have seen this in lots of agriculture markets, timber markets, metals, you name it. In real money terms, crude oil trended downward from 1865 to 1970, and again from 1980 to 2000. I would argue that recent price run-ups are a largely due to politics, not crustal scarcity just as run-ups in the 80s were, but that’s another debate. Another practical reason why oil companies can’t wait to extract is because their contract to explore and produce will stipulate that they get their asses in gear soon, or loose the lease. The owner of the minerals probably wants his royalty check ASAP.
A state resource holder is a whole different animal. Why? A state will often have a much lower discount rate than a firm. This is because states are more patient than individuals (who own private firms) To put it starkly, a person dies while a government theoretically doesn’t. There can be some other reasons to hold back on extraction for a state. Absorption rate is one, especially in a developing country. The marginal utility of money falls quickly in a given period. There are only so many roads, hospitals, schools, etc. we can build this year, no matter how much cash we have, so there isn’t really any reason to sell more than X barrels of crude. Another theory that gets kicked around is that a resource state may actually be working with a downward sloping supply curve. Conventional wisdom tells us when prices are high, a supplier will sell more. However, if a state has a set budget they may produce less when prices are higher to make the same revenue target. (Imagine a youngster just working until he has enough money for a video game he’s had his eye on, and then quitting, no matter what his hourly wage is)
In a “perfect” world, it still doesn’t make a lot of sense for a state to hold off, because they could invest their revenue in a fund for future generations and probably be better off than keeping oil in the reservoir for future generations. Norway and others have a program like this. The world isn’t perfect, however, and such a fund may be hard for the government (or future governments) to keep their hands off of. So, oil in the ground may be safer than cash in the bank.
Hope this helps, let me know if you need some clarification of any points.