For Git ebuilds, please consider passing --depth 1 so that a full copy is not made. With packages like binutils a full clone constitutes a sizeable amount of disk space.
There are some related variables in the eclass: https://gitweb.gentoo.org/repo/gentoo.git/tree/eclass/git-r3.eclass
If you want to avoid full clones, set EGIT_CLONE_TYPE=shallow in your make.conf. We're not changing the default since shallow clones have their own problems.
Thank you both. There is a brief discussion of the limitations in git-r3.eclass. Is there more detail available elsewhere?