Description: The Ingenue is sweet, innocent, and naive to a fault. She's frequently a virgin, and any sort of sexual talk or flirting will go right over her pretty little head. Due to her traits, she's a prime target to become a Damsel in Distress. After all, the hero(es) must save her before anything can damage that delicate flower!
Examples: A fair number of the older Disney princesses, Sandy for a large portion of Grease, Rose from The Golden Girls (oldest ingenue on record?)
Pros: As stated above, they unfortunately make good victims, so there's a way to kickstart a plot. There will always be an audience for "knight in shining armor saves the lovely lass from unspeakable horrors" stories. The ingenue can offer a stark contrast to the hero and highlight his strength and cleverness. In romance, a hero with a tortured past can be "healed" by the ingenue, and who doesn't love a good redemption story?
Or, to put it simply: there are a lot of crappy things in this world. Sometimes it can be heartening to see someone retain their optimism and cheerful nature, despite whatever terrible things may be happening around her.
Cons: If the ingenue is portrayed as too naive, that can translate into stupidity. And if whatever's going around her is really crappy, she can either come across as unbelievable, or you just want to throttle her for not seeming to understand the severity of the situation.
While the ingenue is not necessarily asexual, her "purity" can be quite the hurdle in romantic plots. Some writers like working with that sort of thing. Others don't. (And then that leads to the question - is she still considered an ingenue after the hero deflowers her? Or does her newfound intimate knowledge of intimate matters immediately strip her of that title?)
Would/Did I Use It?: I could be forgetting a minor character somewhere along the way, but no, I don't think I've written any ingenues. Generally, I like my female characters to be strong, smart, successful women. That doesn't mean they're not flawed, but those flaws don't come from a lack of awareness or ignorance of darker matters. Plus, I'm not really a fan of writing sex scenes with virgins.