Libreroot website explains it as following:
Libreboot has been 100% philosophically compatible with GNU, from the day the project was founded (our goal is identical to GNU, and our philosophy is identical to the one held by that project), but there are some technical issues with it that make it incompatible with GNU at present.
Sounds like it's mostly about aggressively reminding you that something is non-free in the universe. The benefits this project provides are stripping out the binaries from the coreboot source while still letting things build. For some of the computers and chip-sets, you might actually be able to use it afterwards.
Libreboot has been 100% philosophically compatible with GNU, from the day the project was founded (our goal is identical to GNU, and our philosophy is identical to the one held by that project), but there are some technical issues with it that make it incompatible with GNU at present.
What exactly does "joining the GNU Project" mean?
Generally tweak the site and documentation, to more aggressively promote the freedom aspect (the main goal of the GNU project). We already do this to a great extent (especially on the home page), but there are obviously areas for improvement. A lot of the time, we assume that the reader already knows about the free software philosophy, without actually explaining it to them properly. We need to fix that. [Announcement]
Libreboot provides a fully free (deblobbed) coreboot tree, called coreboot-libre, with payloads and utilities already included. It attempts to make coreboot easy to use, by providing a fully automated build and installation process (and tested, stable releases), along with documentation designed for non-technical users. You don't even need to build from source if you don't want to; ROM images and utilities are also included in each release, pre-compiled from the available source code. [main libreboot.org page]
Sounds like it's mostly about aggressively reminding you that something is non-free in the universe. The benefits this project provides are stripping out the binaries from the coreboot source while still letting things build. For some of the computers and chip-sets, you might actually be able to use it afterwards.
If you're the type of person who can't compromise on non-free binaries, this probably matters a lot to you. For those of us with filthy enough souls that we're willing to compromise it's likely not going to make much of a difference.