execlineb do not deal with empty word, so a command like
/usr/bin/ntpd -d "" -S
will crash cause of the empty word. execl-cmdline make the same command line to this
/usr/bin/ntpd -d -S
So, it remove the empty word. Also, the -s options split a quoted arguments into separated word like
/usr/bin/ntpd "-d -S"
become
/usr/bin/ntpd "-d" "-S"
Well, taking concrete example. 66 deal with environment file define by a user. Let's say we have an environment file containing this
cmd_args=-d -S
with 2 space between the options, the service without execl-cmdline will crash due of the no word entry.
Hope i'm clear.