Does leaving the Views UI module enabled affect performance? I noticed that the "Disable Developer Modules" link in the Administration Menu module disabled the Views UI module. I'm under the impression that the purpose of disabling the developer modules is to reduce performance impacts. But I didn't think the Views UI module would have an affect on performance. Does leaving Views UI enabled in production have any performance impact? Is there any other reason to disable this module on a production site?
Every enabled module affect performance, just for the fact they are loaded, and parsed from PHP. views_ui.module, in the branch 6.x-3.x-dev of Views, is 10355 bytes.
There are then hooks that are invoked from Drupal, even if you are not using anything from the Views UI module, such as views_ui_help(), views_ui_menu(), views_ui_theme(), or views_ui_library_alter().

Another reason to disable unused modules is avoiding possible security issues.