You would end up with a one side trial balance if you did this.

Example - Payments:

You would credit the bank for the payments, but the system would have nowhere to put the debit. That's why you match before importing - to tell the system where the other side of the transaction is to be posted.

If you mean defer the matching to a later time, there is already the option to see previously unmatched items. You can click this when you come back into the import screen.