When loading transactions into the cashbook, sometimes a single transaction needs to be split into multiple transactions in order to record amounts against different transactions groups. The automatic transaction import process has allowed you do to this either manually or via rules for a long time.
However what has been changed now is the ability to automatically split the transaction based on a percentage of the transaction value. For example sometimes a transaction might need to be split as 50% business expense and 50% personal expense. With import rules you can now specify the automatic split percentage value.