Training at realistic defensive shooting distances is vital if you want to develop applicable shooting skills and truly understand your own abilities. In the moment of a defensive gun use, you should be shooting only when you have the expectation that you will be able to hit the target you need to hit.
Training at realistic distances will help you gain an accurate understanding of your ability to do so. Your most likely defensive shooting distance is influenced by where you spend your time while armed or with access to a defensive firearm. If you only have a gun staged in your bedroom, then you can predict the distance you would be shooting if someone broke through your secured bedroom door to a high degree of certainty.
If you carry a gun in the public space and spend a lot of time out of doors, you could potentially have to shoot to defend yourself over a wide range of distances.
Tom Givens, who ran Rangemaster in Memphis, TN for many years and teaches defensive shooting all around the country, has put a great deal of effort into collecting accurate data on actual defensive gun uses by private citizens. His data, which I trust as the best source for details outside of the law enforcement and military communities, shows that almost 90% of defensive shootings occur between 9’ and 15’. If you think about the distances you would likely need to shoot inside your home, your workplace or even in most public spaces, including around vehicles, this range of distances probably makes sense to you.
There are many anecdotal or myth based pieces of conventional wisdom about the distances you are most likely to need to defend yourself, but I prefer to use facts and logic. Our default training distance in the CFS Program is 12’-15’. You should practice most often at the distances you are most likely to need to defend yourself at, while also working in some practice at both extended and contact distances as justified by where you spend your time while armed.