That's a good point. Actually we don't have any clue about the user/group. 
I think we have two options

1. We remove this behavior. This will leave traces of the application after purging.
2. Make this behavior configurable. 

For _2._ this would need a setting like

```scala
debianRemoveUser := true

debianRemoveGroup := true
```

and question is: What are the _default values_.