Like many life scientists, I see the postdoctoral years as a continuation of scientific training after receiving the PhD degree. Ideally a postdoc should last no more than three years, provide the trainee with the opportunity to acquire several new methodologies above and beyond those learned during the dissertation, result in at least two new first authorship papers and finally provide grounding in grantsmanship.
A postdoc is most definitely not a super-technician (i.e. a technician with a doctorate). As with the graduate student, there is an important mentor-trainee relationship between the laboratory PI (the mentor) and the postdoc. For this mentorship relationship to work, the PI needs to prioritize the training aspect of the fellowship at the same level as the research component. Often that doesn’t happen and it’s a shame. It should.
Additionally, there is a tendency among many post-docs to view themselves as “research assistant professors”. It doesn’t help that some institutions in fact classify postdocs as such. The problem with this self-image for the trainee is that the education component of the fellowship also becomes de-emphasized (any many PI’s have no problem with it). There may be the further problem of the trainee and PI getting at cross-purposes over who “owns” the research produced during the postdoc.
These days, a scientist may have several postdocs before going on on the job market. That’s OK within limits. Each postdoctoral fellowship should add new techniques, new scientific perspectives and increasing independence. And they should be in different laboratories lest the trainee eventually turn into a super-tech.