Author metrics track how often an author's work is cited by other researchers. They are long established form of metrics.
Author metrics are utilized in grant applications, tenure, promotion, and performance reviews in some organisations.
They can also be used to discover key researchers in a field, track colleagues' work, and identify potential collaborators.
Each citation count is likely to different results as alternative database use divergent sources. Therefore it is is best practice to use more than one method to evaluate an authors impact.
This page lists relevant metrics that assess an author's impact. This is not a comprehensive list of metrics as new metrics are becoming available all the time.
Google Scholar is useful for international coverage because it tracks all types of scholarly publications on the internet. A limitation of this resource is that it is unknown which sources are indexed and when.
Scopus is used in the sciences (sciences, engineering, medicine) rather than for others sciences (social sciences and humanities). A limitation of this resource is that only publications connected to Scopus are included in the citation counts.
Web of Science is used in the social sciences and humanities. A limitation of this resource is their uneven coverage of certain subjects in terms of coverage and dates.
Author Metrics do not measure the number of times a work has been read or accessed. These are important measures of a works impact.