Why the LinkedIn Headline is so Critical in a Job Search?

Because of the following reasons:

1. Gives precise definition of What you are and What you are searching for
2. Makes your Profile relevant and interesting to your market audience
3. Generate strong Keywords which in turn produces more search engine indexability and hence greater visibility

LinkedIn Headline forces people to present themselves in just 120 characters. Hence they have to think a lot about what they are going to say, since the Headline is what everyone sees even if not connected.