When you are deciding how to use metrics information (e.g. to apply for a grant or promotion), it can be helpful to understand how citation data is regarded in your particular discipline.
Excellence in Research for Australia (ERA) is a framework administered by the Australian Research Council to identify and promote excellence in research.
The ERA 2018 Submission Guidelines explain a key distinction between citation analysis and peer review (p.15):
Citation analysis: an indicator of research quality in disciplines where there are sufficient outputs in indexed peer-reviewed journals to allow robust citation analysis.
Peer review: in disciplines with more diverse outputs, [where] journal citation analysis may not be sufficiently robust..., peer review of a sample of outputs across all output types is the indicator used.
The disciplines where ERA assesses excellence based on citation analysis, and those where peer review is relied on instead, are shown on the 2018 ERA Discipline Matrix according to Field of Research (FOR) Code (see the second column, headed Journal Article Citation Analysis).