Continuous CAD means we're always requiring foreign investment inflows to the Capital and Financial Accounts, which in turn means high servicing requirements and all the associated debt/liabilities issues. It makes us more vulnerable to conditions in the global market, and maintaining the perception of external stability is important because we cannot afford investors to lose confidence in our economy. There's the debt trap scenario (cycle of debt, whatever) where high CAD leads to high foreign debt which leads to high CAD etc etc. Also having high CAD and debt could lead to low credit ratings hence making life difficult to borrow funds.
But, yes there should be plenty of extrapolation in your textbook.