Most of the time you want $@. But a use I've found... Let's say you're creating a script that creates another script (e.g. to be executed on a remote server). You have an array with commands, and you want to pass $@ to the command:

f() {
    cmds+=("some-command ${@@Q}")
}
f a b c

But this way 3 elements are added to the array: some-command a, b, and c. What you want is:

f() {
    cmds+=("some-command ${*@Q}")
}
f a b c

Most of the time you want $@. But a use I've found... Let's say you're creating a script that creates another script (e.g. to be executed on a remote server). You have an array with commands, and you want to pass $@ to the command:

f() {
    cmds+=("some-command ${@@Q}")
}
f a b c

But this way 3 elements are added to the array: some-command a, b, and c. What you want is:

cmds+=("some-command ${*@Q}")

Or even:

cmds+=("some-command${@+ ${*@Q}}")