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Pro Allows to be officially systemd-free
Gentoo's default init system is OpenRC. Gentoo also officially supports systemd-free Gnome and udev.
Pro Portage's emerge is powerful
Pro Full control of the software
Pro Gentoo does not impose a standard look-and-feel
Pro A very large collection of software is available
Pro Great for anyone who is serious about learning the intricacies of Linux
It's useful for both beginners and professionals. For the installation, Gentoo offers various types, which are referred to as stages. Basically meaning how in depth you would want to go into the process of installation. For beginners it's useful to choose for a starting distro due to its various stages that can be very time consuming but beneficial as you learn the composition in general of Linux.
Pro Documentation and community are second to none
Pro Live USB
Con Customized package installation can take a long time and cause installation failures
The Gentoo package management system allows you to configure what compilation flags packages should support - i.e. specific processor flag support (SSE, SSE2, etc.), -O1, -O2, -O3 optimization, etc.
If you accept one of the default flags, Gentoo downloads binaries from the server. However, if you decide to optimise, it can and will download all source packages and start compiling ALL the programs and libraries on your system. If your chosen flags don't work with a particular library, installation will fail.