At the moment in JIRA work can be logged by any user (with permission), no matter who the assignee is or what is the state of the issue. I would expect that in most cases, only issues in progress can have work logged on them, and only the assignee can log that work. This would reduce the room for error when tracking time / logging work. These restrictions could be optionally (for those people that may want to log the work involved on closing an issue, for example) enabled/disabled by the administrator.