Move" tells Transformer to include a category under the latest-encountered parent in the event of a uniqueness violation rather than generating an exception. A classic example would be a salesperson who has moved from one region to another...if Transformer encounters sales data for that employee in region "East" and then in region "West", all sales would be reported under "West".
Note that "latest-encountered" does not imply consideration for the time dimension, it's simply based on the order in which the records are read - for recasting history to the current state you would want your query sorted chronologically.