I actually didn't really know about the difference between $@ and "$@" until now.
I always had assumed that "$@" is not desirable thinking this would deliver argsments as just one.
Turns out that's not true and you can read about it from man bash.
@ Expands to the positional parameters, starting from one. In contexts where
word splitting is performed, this expands each positional parameter to a separa
te word; if not within double quotes, these words are subject to word splitti
ng. In contexts where word splitting is not performed, this expands to a single
word with each positional parameter separated by a space. When the expansion o
ccurs within double quotes, each parameter expands to a separate word. That is,
"$@" is equivalent to "$1" "$2" ... If the double-quoted expansion occurs withi
n a word, the expansion of the first parameter is joined with the beginnin
g part of the original word, and the expansion of the last parameter is joined
with the last part of the original word. When there are no positional parameter
s, "$@" and $@ expand to nothing (i.e., they are removed).
And you can easily test this
# desirable usage
$ cat <<EOF | bash -s - "single" "multiple chunk"
for i in "\$@"; do echo \$i; done
EOF
single
multiple chunk
# probably undesirable usage without quote
$ cat <<EOF | bash -s - "single" "multiple chunk"
for i in \$@; do echo \$i; done
EOF
single
multiple
chunk