Why do highway department put up "Guardrail Damage Ahead" signs?

Is it just for informational purpose so that you can see what will happen to you if you run into it?

Is there some kind of study that shows that people who are not informed of the damage will unexplainedly drive into them again?

Did some lawyer decide that they would be liable if someone hit an already damaged rail but not if they could say “Hey, we told you it was messed up”?

Why just they don’t just fix it?

Why does each good rail not have a sign that says “Good,
Usable Guardrail Ahead”?

Just curious.