That's it. Software from the regular repositories, including Extras-Testing, should be optimized to leave the rootfs alone. (There have been some exceptions.) Stuff from Extras-Devel or other sources almost certainly is not. (Some in devel might be.) So if your rootfs is getting full, removing packages installed from devel or outsides sources should free up some space. You may or may not need to reboot after removing them for the system to properly recognized the rootfs size.