We're using New Zealand as an example of MMP, and of course, it's important to acknowledge that there are many variants. When we talk about an electoral system, the details really do matter.
Local voters have two votes, right? They get to vote for the person they want to be their local MP and for the party they want to govern, separately, and we see that in many cases they split those votes. Using the example of Auckland Central, a downtown Auckland riding, in the last election Labour received 44% of the MP vote, the electorate vote. They lost in a very close race to a National incumbent, but they only received 22% of the party vote. This is really important, because it's the party vote share that determines how many seats they end up with in the legislature, not the electorate vote.
From the party's perspective, they want to try to maximize the party vote, but you can imagine that the local candidates and the local members in Auckland Central and other places, especially if they're incumbents, want resources to get them re-elected to be the local electorate MP. It has created real tension in the party. That's why they've just moved—it'll be used in the next election for the first time—to these sort of regional hubs, where they hope to put a lot more resources and emphasis not on the local electorate but sort of regionally, to try to get people to vote for the party to maximize their share of the vote on that part of the ballot.