You've been charged with a rather serious criminal offense -- and the prosecutor talked about "throwing the book" at you. You're naturally surprised, then, when you're suddenly offered a plea deal that seems much better than the sentence you expected to receive if you lost your case at trial.

What's going on? Is the prosecutor's case actually so weak that they need to resort to a plea deal to win a conviction? Maybe -- and maybe not.

The vast majority of criminal cases never go to trial, even when the charges are serious. That's largely because everybody involved -- the prosecution, the defense and the court -- has some incentive to cut a deal.

For defendants, the advantage of a plea deal is that it gets a case over with quickly, without much uncertainty when it comes to sentencing. Many people find it easier to cope if they end the gamble with their future through a plea. The odds are also good that a plea deal will involve reduced charges, a reduced sentence or both.

For prosecutors, the plea deal is an easy win since a plea equals a conviction on the books. They also save time and effort, which is a big deal when they have a lot of cases pending. Plus, they may want something from you in exchange for the deal, like your testimony against someone else.

The courts also like plea deals because it eliminates a lot of costs and helps ease the backlog the judges are facing.

None of this means that a plea deal is actually in your best interests. To know that for certain, it's wisest to speak with an experienced defense attorney about your case.