I have certainly heard of this tactic used when trying to get homeowners' liability coverage for a shooting. Shooting someone, even in justified self-defense, often results in a civil liability suit. When this happens, people turn to their personal liability insurance for coverage. However, most homeowners'/renters' liability policy exclude coverage for 'intentional acts'. There have been many appellate court cases across the country finding that shooting someone is an intentional act and therefore there is no insurance coverage.
But there have been findings of coverage for accidental shootings. In some states, and depending on the specific fact pattern, if you can convince the Court that you shot someone by accident, you might get liability insurance coverage for this. It rarely happens, but it might be worth a try, depending on the case law in your jurisdiction.
In the criminal context, I would imagine that claiming it was an accident means that you had no intent to shoot someone, and therefore you might get a lesser charge, such as manslaughter or negligent homicide, which generally carry less severe penalties for a conviction.
