Another way of looking at it - if you have both cash and equity (ie LOC), as well as non-deductible debt, then never buy investments or tax deductible expenses using cash - use your LOC, leaving the cash to offset or pay off the non-deductible debt.
Cash sitting in a normal bank account is useless - it must either be in an offset account, or payed off your non-deductible PPOR loan.