In many cases developers of one project use their own local environments for coding. There may be a common test platform and, of course, production. All these environments usually have different DB credentials and directory structures (first of all, path to YII framework directory). Another feature is debugging. It's convenient to turn it on for local environments, eventually - on the test server and never (generally speaking) - on the production.
If you develop your Yii project on both Windows and Mac, there can be a problem setting up the configuration unless the configurations for both system are identical.
On my machines I have the following configurations: