It can do the same things as open carry but without signaling “I have a gun”. Those things can be useful separate from the statement made by open carry. Example: you can kill someone that is a serious threat to you but can also avoid intimidating people you’d rather not intimidate.

IMO the usual non-reactionary reason to carry at all is that you live in a place where dangerous situations come up often enough that you feel the need to have the ability to shoot aggressors to protect yourself and your community. Someone wants to rob you or a neighbor by pointing their own gun to your temple. Someone starts swinging a pipe at you haphazardly and won’t stop. Someone much bigger than you keeps trying to fight you. “Stealth” is often perceived as valuable in this environment. You will have to surprise the aggressors. It’s also harder for someone else to grab your gun from its holster.

Open carry is still very useful, especially as part of an organized cadre protecting an action. One or two people open carrying at an action become targeted by cops. A group of 7 is a deterrent and the cops actually tend to act more cautiously.

When someone attacks you or another person with the intent to fatally injure?

To each their own.