First of all, what do I think of when I say the oracle feature. It could be said to be any power, entity or device that allow the character to ask for advice/guidance for a supposedly all knowing entity. I'll give a few examples:
WOD: The merit foresighted or oracular ability- allow the character to attempt to get a vision of the future.Why do I think this is so beneficial? I should be honest and say that they are a great fun, to play and just as funn to see the players ponder the answer. Well that was why I like them, not what they do for the campaign.
D&D 3.5: The spell commune - allows the character to ask one or more questions, and get an answer, from a deity.
Any setting: A Oracle - a person/entity that the character may seek out and ask questions about the future for a price. This could also be a person that is not all knowing, but know significantly more than tha characters.
They function as a sort of emergency escape hatchet form prolonged deliberation or standstills. By that I mean that when the players are at a total loss of ideas for what they are to do they might seek out the oracle feature. Or when they can not decide which choice to make in a certain situation they can seek the oracle feature to help make a decision.
I have heard of games that have fudge-points or other game mechanisms for prompting the game forward*. These are as the oracle feature something that the player initiates. The main difference between fude-points and the oracle feature are that the oracle features also can be represented in the setting as a natural element.
Foot Note:
* I admitt to having used this once in Legend of the Five Rings. After achieving some great victory I awardws one player a Divinity Point that he could use to great effect. A few sessions later he cursed an entire city to insomnia. Well the curse was that those that had anything to do with the opiumtrade would be unable to sleep. Did I mention that the city he cursed was the empires center for opiumtrade? It was awsome. Having said that, the Divinity Point could have been an oracle feature if the player chose to, but he chose to use it to fule his curse instead.