Nah I don't think there is any benefit to the user.
The benefit comes from them being able to work together to get deals with content providers, Spark seem to be taking the idea of Internet TV pretty seriously and want to be the leader in NZ, this way they get a partnership in Sports Streaming without having to front up themselves. I think it is more about "alignment" than anything else.
This deal made a lot of sense for them with the rights expiring at the end of this season too. It is likely sky will use their spending power to price them out of the market (even at a loss to themselves), but with Spark on board they now have the resources to match sky and actually have more incentive than sky to pay too much for the rights.