The javadoc for the DataStream#assignAscendingTimestamps

`* Assigns timestamps to the elements in the data stream and periodically creates
 * watermarks to signal event time progress.
 *
 * This method is a shortcut for data streams where the element timestamp are known
 * to be monotonously ascending within each parallel stream.
 * In that case, the system can generate watermarks automatically and perfectly
 * by tracking the ascending timestamps.`

This method assumes `that the the element timestamp are known to be monotonously ascending within each parallel stream`. But in practice, almost no stream can give such guarantee that event timestamps are in ascending order.

I would like to conclude that this method should never be used,but I would ask if I have missed something(eg, when to use it)