The plus with this is that your preferences will never boost a candidate you don’t support. Quite simply, if you haven’t numbered a box beside a candidate’s name they can’t get your vote.
The minus is that it tends to secure the position of the two major parties in government because they often recommend putting a 1 beside their candidate and leave all the other boxes blank, as the Liberals and One Nation have done in Camden this time around.
Those party recommendations that rusted on voters follow religiously, coupled with the laziness factor, (I can’t be bothered marking more than one box), means that the primary vote in NSW often decides the wining candidate (ABC’s Antony Green explains it beautifully here). It’s why we have so few crossbenchers and Independents in NSW compared to other Australian states.