also lets you delete stuff.
# analyze current working dir, stay in the same filesystem
ncdu -x
# run this on the thingy that builds binary packages to
# rebuild the metadata index
emaint binhost --fix
# delete source for anything without an ebuild in any repos
eclean-dist
# delete source for anything that isn't installed
eclean-dist -d
# delete binary packages from /usr/portage/packages for anything
# without an ebuild
eclean-pkg
# delete binary packages from /usr/portage/packages for anything
# that isn't installed
eclean-pkg -d