Numbers are used in all sorts of scholarly works. For example, writers may report numerical information about participants (number of participants, demographic information such as age, etc.) as well as the results of statistical analyses.
Even writers who are not conducting empirical research often use statistical information to support key points. For example, writers conducting a literature review or writing a response paper may report numerical information such as the percentage of people diagnosed with a particular disease or disorder, the staffing levels of psychologists or nurses, or the number of terms on a topic they were familiar with.
When writers follow guidelines for number usage, their papers become more consistent and readable.