Why (src_prepare)

Why use Gentoo?

Optimization ( packages can be compiled for a specific CPU, ex.: -march=haswell )
Customizaton ( USE flags )
Version mixing ( specific versions of software can be masked or "accepted" to use bleeding edge )
Lack of trust towards binary packages provided by a binary distro
Ability to "package" almost anything ( ebuilds )
Recompiling software from git when new changes are pushed ("live" 9999 ebuilds)
OpenRC - lightweight and flexible init system
eselect - system configuration framework (a bit similar to dpkg-reconfigure)
webapp-config - web application installation framework
XPAK - new way of binary packge distrubution
Free as in freedom ( ACCEPT_LICENSE can exclude nonfree software )
Is a Linux ( not necessarly GNU ) distribution
Hobby