Way back in the day (and in some places still nowadays), people learned marketable skills through apprenticeships. They worked under the direct tutelage of a master, observing and absorbing skills as they went. I've compared graduate school to an apprenticeship in the past, and I still believe that science, for all of its fanfare and academic regalia, boils down to an apprenticeship system.
A recently-graduated apprentice does not become a master straight away. First, they must hone their skills and develop their own unique style. In the Middle Ages, apprentices who had recently finished their training traveled the countryside, seeking work wherever they could find it. I suppose nowadays we would call them free-lancers, but the proper term is actually "journeymen."
Friends, if graduate school is an apprenticeship, then a post-doc is a journeyman - one who has spent years observing a master, has completed all the required training, but is still not a master themselves. They travel the world seeking work, sharpening their minds, and developing their own unique projects.
I've told you I'm networking my way through WHOI right now, getting to know other researchers at my institute and planting seeds for future projects. I feel very much like a journeyman, tasked with developing my own unique style as a scientist. I'm grateful for the mentors around me, who nudge me in the right direction, making sure I will be fundable in the future. I have a phenomenal advisor who has already helped me start crafting a scientific persona. Someday, I will be a master.