Citation databases assist in the evaluation of publishing activities. They can be used to find out the volumes of publications and references and consider, e.g., which are the most referenced articles or journals. However, referencing itself is not always a quality criterion and there can be several reasons for referencing (negative references, ethnocentricity, self-references).
Citation analysis is used in the evaluation of research. Based on citations, one can evaluate scientific journals, individual researchers, research groups, disciplines, research institutes, universities and entire countries. For example when citation analyses are used in recruitment process, researchers must be aware of data concerning themselves.
Also, the researcher needs information about the number of articles he writes and the most cited publications, like in grant applications, CV, etc.
The main databases containing citation data are the multidisciplinary Scopus (Elsevier) and the Web of Science (Clarivate Analytics). Citations can also be searched from the freely available Google Scholar, as long as you remember its limitations.
It is not possible to make cross- disciplinary comparisons. The reasons are differences in the most typical formats of publication, the rate of accrual of citations, and the prevalence of joint publications.