This template is for use in articles where a short citation does not contain enough information to allow a reader to tell easily which long citation the short citation is referring to. For example, if there are two books in the references section by the same author, unless there is a year of publication of some other information in the short citation a reader will not know which book contains the cited information.
This is the sister template for {{full citation needed}} which used to request more details on a full citation. If all that is missing are page numbers then use {{page needed}} rather than this template.
This type of error often creeps in because initially in the references section there is only one book by the author John Doe, so a short citation containing "Doe p. 4" is just enough to link the short citation to the long reference in the references section.
Then another editor comes along and adds more information by the same author, but to a different book (possibly only another edition). The editor adds a new short citation and a new entry in the References section. That editor includes with the new short citation a year ("Doe, year, p. 17") so that it is clear which long reference in the references section the new short citation refers. The problem is that for people who now read and edit the article the earlier short citation "Doe p. 4" does not now contain enough information to make it clear to which long reference in the references section the old short citation refers.
To help avoid this problem occurring in an article at a later date, it is better to include author and year when creating the initial short and long citation pairs even if the year is not necessary to uniquely identify the pair.
