'$YAST_IS_RUNNING" != "instsys" is used in some rpm .spec %post sections

It is also used in: /usr/lib/rpm/suse_macros

I would like to know when and why it is used because I need to add:
%regenerate_initrd_post
in some packages %post section.

And especially there it is often embedded into:
if [ "${YAST_IS_RUNNING}" != "instsys" ]; then
 if [ -e %{_localstatedir}/lib/no_initrd_recreation_by_suspend ]; then
   echo "Skipping recreation of existing initial ramdisks, due"
   echo "to presence of %{_localstatedir}/lib/no_initrd_recreation_by_suspend"
   %regenerate_initrd_post
...

But this seem to be old and I wonder what for or whether it is needed at all
anymore.