Note that every article on Wikipedia has a General disclaimer indicating that the article contents may not be accurate. As such, this template is redundant.
As an advisory to editors, it may also be used to indicate that an athlete should not be affiliated with a team without referencing an official announcement. Unofficial reports from reliable sources, if mentioned, must be attributed to the news source (e.g. "ACME News reports that John Doe was traded ...").
Generally it is expected that this template and its closely related templates will appear on an article for perhaps a day or two, occasionally several days, until the transaction is officially confirmed, denied, or does not materialize.