Labour has the numbers to govern alone, but the decision to keep channels open with the Greens' leadership through ministerial portfolios outside Cabinet is a good one in different ways.
At a basic level, it's a sensible arrangement between two parties that have policy interests and values in common.
Climate concerns will only grow in importance. As a country New Zealand needs a smart approach and this is a way of adding more talent and ideas into the mix.
Common goals in the agreement include: "Achieving the purpose and goals of the Zero Carbon Act through decarbonising public transport, decarbonising the public sector, increasing the uptake of zero-emission vehicles, introducing clean car standards, and supporting the use of renewable energy for industrial heat."
From both parties' viewpoints the deal will be a constant public reminder of the large mandate the centre-left bloc has established. On the provisional count that's 56.7 per cent of the election vote and 74 seats, compared to the opposition bloc's 35.8 per cent and 46 seats.
That matters in the public debate over future policy initiatives. In lobbying over ideas, the loudest voices aren't always representative of where most voters are at.
The deal is also a nod to one of the strengths of New Zealand's proportional political system, in that it allows for areas of co-operation rather than being endlessly adversarial. A pact enables extra stability.
Both parties gain something in the dance between being work mates and rivals.
For the Greens, the party gets an avenue for its ideas but also enough distance to maintain its own identity.
That's better than sitting in opposition, unable to influence policies. It also means there's less risk of being swallowed by the dominant partner, which can happen in formal, close coalitions, as the party looks towards the next election. Both parties can get credit.
For Labour, it gives more control over the relationship between two parties that essentially occupy the same turf.
A smaller rival party is more problematic for the major party when it is dissenting publicly in opposition. It provides an outlet to people who might feel frustrated with how the major party is handling an issue. It can outshine the more mainstream party. For Ardern, it also lessens the chance of volatile factions developing among her large intake of MPs.
In terms of benefits for Ardern, the move comes across as generous as it is something she didn't have to do. It is also a sign of wanting to occupy that John Key space of being the clear face of the Government people connect with, slightly removed from the squabbling below.
To maintain public support for the Government she needs the widest number of people to feel represented in it.
Climate policy is also a tricky pathway for the Prime Minister. This sends a message she wants to take it seriously and make it work.
To maintain personal popularity long-term, she will need results and progress that she can point to in this key area. That means incorporating good ideas and competent people.
