This is used to differentiate between (with `ess-dont-vertically-align-closing-paren nil`):

```
foo(a,
    b,
    c
    )
```

and (with `ess-dont-vertically-align-closing-paren t`):

```
foo(a,
    b,
    c,
)
```

As you said before, this could be made more clear.