A cross transaction which brings about a change through an inflow/outflow of fund involves a current account and a non-current account.
Of all the transactions that take place in an organisation during a period, the number of transactions involving non-current accounts would be far lesser than the transactions involving current accounts.
Therefore, in identifying cross transactions it would be easier to look out for transactions involving non-current accounts and then looking out for cross transactions within them rather than going through all the transactions.