After changing SMARTD_SAVESTATES and/or SMARTD_ATTRLOG to "no"
/usr/lib/smartmontools/generate_smartd_opts writes a new file
/var/lib/smartmontools/smartd_opts.
The value of smartd_opts in this file is appended to the smartd command by

-------------
EnvironmentFile=-/var/lib/smartmontools/smartd_opts
ExecStart=/usr/sbin/smartd -n $smartd_opts
-------------

in smartd.service.

In /usr/lib/smartmontools/generate_smartd_opts the corresponding parts are

-------------
if test "$SMARTD_SAVESTATES" = "no" ; then
    smartd_opts="$smartd_opts -s \"\""
fi
-------------

and

-------------
if test "$SMARTD_ATTRLOG" = "no" ; then
    smartd_opts="$smartd_opts -A \"\""
fi
-------------

which generate no valid command line option for smartd in
/var/lib/smartmontools/smartd_opts.
The result is smartd.service failing to start.


I tested with the following changes:

-------------
if test "$SMARTD_SAVESTATES" = "no" ; then
    smartd_opts="$smartd_opts -s -"
fi
-------------

and

-------------
if test "$SMARTD_ATTRLOG" = "no" ; then
    smartd_opts="$smartd_opts -A -"
fi
-------------

which generate the valid command line options  "-s -" and/or "-A -".
smartd.service starts and the corresponding logging is disabled.