Gentoo and FreeBSD

[Sean]

I came across the Gentoo/FreeBSD project at 
http://www.gentoo.org/doc/en/gentoo-freebsd.xml

A description states
What is Gentoo/FreeBSD?

Gentoo/FreeBSD is an effort to provide a fully-capable FreeBSD operating 
system with Gentoo's design sensibilities. The long-term goal of the 
Gentoo/BSD project is to allow users to choose any combination of *BSD 
or Linux kernels, *BSD or GNU libc, and *BSD or GNU userland tools.

What exactly does this gain a user?
Use of both Linux and FreeBSD fully, partially, some sort of mutant 
creature?

FreeBSD is a complete from top to bottom, so again, what does this combo 
  do for a user?
Would this gain something else instead of having linux support enabled?

			Thanks
			Sean