At ALTLinux, much effort is put into maintaining accurate spec-files for packages and that building the packages is accurately reproducible in the current state of the repository of packages. It is being checked regularly that every package in the repository (called Sisyphus) is rebuildable at the current moment -- a rebuild test status report, the logs of the last rebuild test, per package.
To be sure in accurate reproducibility of package builds, special tools to isolate the build system from the host system are used: hasher and the surrounding build-infrastructure tools (e.g., Building packages with gear).
So, although ALTLinux isn't dedicated to installing your system by building, one can be sure that a package he takes from the repository will be easily rebuildable at his host system, without extra issues that haven't been tracked formally by the spec.
ALTLinux is dedicated to being the source for custom package repositories and distros, which--by the design of ALTLinux build system and associated tools--can be easily customized and rebuilt independently from ALTLinux and safely (i.e., isolated from your host system). So, if one wants to make his own customized distro, ALTLinux Sisyphus can be the base for this distro that will be easy for him to use in his work: Intro into making your own distro (in Russian).