Gentoo Linux is a source-based Linux distro that uses the Portage package management system.
It is not meant for Beginner Linux users, but rather Intermediate and Advanced ones who are familiar with the command line and kernel compilation (because, during install, the user will have to compile the kernel herself).
Packages (through the Portage system) are also distributed in source form, and compiled to binaries on the user's system upon fetch and installation. The Portage system is smart enough to automatically fetch (and compile) any dependencies a package needs before it gets compiled.
The benefit of Gentoo Linux would be a highly customized -- and thus potentially higher-performing -- system that matches exactly what the user has, without the baggage of unnecessary code that makes the system bigger and/or slower.