I got this far without it, I'll take my chances
Most gun owners put an awful lot of thought and work into our guns, how to own and use them legally, and even how to prepare for self defense. But most gun owners have no comprehensive plan how to deal with the aftermath of armed self defense.
Unfortunately, even when you have legally and justifiably used a firearm in self-defense (even if you didn't fire a shot) you may have to defend yourself a second time in the legal system. You can't depend on the law enforcement system to protect your rights or justify your self defense. Their job is to investigate and place blame.
You will be investigated and can be arrested. You'll have to immediately find a gun rights attorney, money for bail and attorney retainer, and begin a defense against criminal charges. Self defense, castle doctrine and stand your ground are legal "defenses" not get out of jail free cards.
You can lose your job and get bankrupted by legal fees. You could spend years in jail. Without a proper legal defense and the money to pay for it, you could literally lose everything.
Even if you're not charged, the charges are dropped or you win the criminal case, you can lose your home, savings, and personal property in a civil case by the criminal who attacked you, or by the surviving family. They have nothing to lose and you have everything to lose. It seems the legal system almost encourages them, especially the "I get a share" attorneys.
In the gun magazines and websites, Massad Ayoob and others, often write about the cases of justified armed self defense where the defender winds up investigated, charged, prosecuted, jailed or sued. They often recommend, as part of your self defense plan, to have a legal program in place that will deal with the aftermath. The worst plan is "I'll take my chances".