That's not correct. It's for people who think they might be targets of surveillance operations, like journalists and activists.

> Lockdown Mode is an optional, extreme protection that’s designed for the very few individuals who, because of who they are or what they do, might be personally targeted by some of the most sophisticated digital threats.

(from https://support.apple.com/en-us/105120)

This is mostly useful if you run it all the time, since you generally won't know when you will be targeted.