In nearly all movies involving "gangsters" with guns, you're bound to see the firearm cocked sideways. It was even a joke in the movie Date Night where Steve Carell's character calls this position the "kill shot."
A former U.S. Marine Corps marksmanship instructor thinks there could be some merit to that logic, according to the Daily Mail.
In an effort to save time, make a getaway and maintain some accuracy, Davis said the method being used is called "flash sight picture," which aims down the side of the gun. It isn't necessarily the most precise, but it can get the job done.
The Daily Mail reports finding Davis' thoughts on this shooting style from the site Quora.com. On it he wrote:
The problem with tilt style shooting is that it is almost impossible to acquire a reliable sight alignment. The alignment in tilt style is achieved by making the weapon flat and aiming down the side.
In theory this works, but in practice you can't accurately measure movement left or right and you have absolutely no way of knowing if the weapon is tilted down below your field of vision from the back of the weapon.
This means that you never actually take the same shot twice since you are never actually aiming the same way.
Overall, Davis writes he would not recommend this tactic because, although he calls it good in theory, it "fails miserably in the actual execution."
The technique for proper shooting that Davis recommends is called "building a castle." He writes on the site that the castel is built by "lining up the three 'turrets'" --that is the turrets on the top of the gun -- with the intended target, making sure they are level and evenly paced.
Check out more of Davis' explanation for why the gun is sometimes held sideways in films here. The person asking the question in the first place speculates the technique has taken on a "kind of 'hipness'" at this point.
If you're intersted in seeing the "kill shot" from the 2010 Date Night, check out the movie trailer, skipping to 1:09: