If you are a New Zealand resident it can be difficult to see a benefit in repaying your student loan debt faster than you need to. But not doing so exposes you to risk. The right wing end of the political spectrum makes regular calls for interest to be reinstituted for New Zealand residents. With a deteriorating economy, it is easy to envisage a situation where a centrist Labour or National government feels it has no option but to charge interest to all borrowers. Or the government could change the repayment rate from 12% of your income to a higher amount.
Having any New Zealand student loan debt can make moving overseas a financial disaster. It also impacts on your ability to borrow to buy a house.
We need to stop thinking that a no interest student loan debt is harmless. It has the potential to ruin your future financial life. The only safe option is try to repay the loan as soon as possible (or to consider bankruptcy if there are no other options).