This is most useful in fields whose works are commonly known by their date of publication (for example, the sciences and social sciences in which one cites, say, "the 2005 John Hopkins study of brain function"), or if the author cited is notorious (for example, HIV denialist Peter Duesberg on the cause of AIDS).
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According to an 1896 paper by Charles Sedgwick Minot of the Harvard Medical School, the origin of the author-date style is attributed to a paper by Edward Laurens Mark, Hersey professor of anatomy and director of the zoological laboratory at Harvard University, who may have copied it from the cataloguing system used then and now by the library of Harvard's Museum of Comparative Zoology.