It is far cheaper than subsidising an increasing number of childcare centres, some of dubious quality.
To my mind there is common sense in the usual right-wing arguments about having the number of children you can afford, taking financial responsibility for them where you can, and not leaning on welfare more than strictly necessary. I believe most people actually do follow these broad principles when growing their families.
But the reality is that you cannot dictate who has children, how many they have, or when they have them. So-called 'bludgers' will always make up a percentage of those putting their hands out for help - I'm sure its offset by those who don't claim PPL, continuing to work around their babies as it's more lucrative. Most cases where PPL is paid are, surely, families wanting to do a good thing for their children.
If New Zealand extended paid parental leave of six months, even a year, to, say, each woman's first two children (I personally think this would be entirely fair), revamp and reinforce Plunket with proper funding, strictly monitor and actively promote quality childcare from the one year mark, and look to back/promote industries that are flexible and allow parents real options about combining work and family when their one year is up, my belief is that everyone in society would benefit, not just families with children.
It's not going to happen in the current political or economic environment though.