to make debugging Makefile easier.
For example:
# make RELEASE=3.1 obj
# make RELEASE=3.1 TARGET_CD_IMAGE=sgimipscd fetch
# make RELEASE=3.1 TARGET_CD_IMAGE=sgimipscd
or:
# make RELEASE=current obj
# make RELEASE=current RSYNC_SITE=rsync://rsync.NetBSD.org/NetBSD-daily/HEAD/200702280002Z TARGET_CD_IMAGE=macppccd fetch
# make RELEASE=current TARGET_CD_IMAGE=macppccd
etc.