revising documentation for proportional spacing

[Werner LEMBERG]

While revising the documentation for proportional spacing in the NR I
stumbled upon

```
\override PaperColumn.used = ##t
```

that gets mentioned without any explanation.  Looking up some
discussion in `lilypond-user` from 2006

  https://lists.gnu.org/archive/html/lilypond-user/2006-12/msg00107.html

it seems that it was necessary then.  However, the examples given in
these e-mails seem to work just fine with 2.25.13 if I omit setting
the `used` property.

Does anybody know more?  Can someone confirm this observation?


    Werner