That does not work in practice. Consider

    void foo() {
        connect(this, action,
                that, callback);
    }

If the "that, callback);" line was indented with tabs, then any other tab length would make it go at any random place. Thus if you just use tabs your code is only readable with the tab length used for writing it. So instead you can introduce spaces for alignment ; now that you have spaces needed for alignment, why not just use spaces for everything instead of two characters ??