From what I can tell, it's a good thing.

Currently, Gentoo is managed and run by the Gentoo Linux Foundation. The GLF is a non-profit whose job it is, is to run the day to day of the business side of Gentoo operations (management, taxes, marketing, etc along with developers to develop Gentoo).

The SPI is a larger non-profit that does the same as the GLF, but at a greater scale. They will focus on the day to day allowing the engineers to focus on developing Gentoo. They also can provide funding from a greater pool of donations and manage taxes and the like.

SPI also helped other foundations like the Debian Foundation and other open source software as well.

TL;DR: the paperwork is being done by a bigger entity, saving them money and providing more resources while allowing Gentoo to focus on developing.