Current theories regarding the evolutionary significance of anxiety and fear suggest that

I believe the answer is: They focus is on adaptation to many situations. They help mobilize responses that help the person survive in the face of both immediate dangers and long-term threats.

When people experience fear and anxiety, we tend to step back and become hesitant in making our decision.
During this process, we would eventually examine all the situation at hands and carefully construct the best possible action. This would help is in handling dangers/threats around us.