When establishing yourself as a researcher, the importance of independence from your PhD supervisor and focusing on a niche area (to establish popularity in a particular sub-field) are fairly well-established. For longevity of research career the polar opposite criteria of collaboration and breadth have been suggested.
Defining the terms field and subfield etc. is important, so taking the following hypothetical example:
Subfield - PhD research uses a common computational method applied to a number of closely related problems.
Related Subfield - Other PhD students in the group apply the same method to different problems.
Field - Computational methods related to PhD yet distinct applied to any problem in the super field
Superfield - Broad area of research encompassing theoretical, computational and experimental work, eg superconductors, photonics, etc.
After PhD and prior to tenure, how specialised should one aim to be and how closely related to the PhD should the specialty be?
If given the choice, is it best to focus exclusively on a related subfield topic (generally project based research typical of most post doc positions), or take on another topic in the field, or to develop breadth by researching multiple related sub field topics in collaboration with other groups?