Think of this as an alternative to set -e in bash. What it would do is abort the whole script, if a single line fails.

This is useful in cases like this

import foo
do_some_magic
import bar

in this case you definitely don't want to do_some_magic if import foo fails.

It might also be good to have this option available just for blocks, so that you could do

some_magic

begin -e # or whatever the switch will be
  first_thing  # if this fails, the whole block will exit
  second_thing
end

some_more_magic

Using and is not a solution for more than two commands, as it pollutes the script, makes it harder to refactor, etc.