Preference variables affect the Windows PowerShell operating environment and all commands run in the environment. In many cases, the cmdlets have parameters that you can use to override the preference behavior for a specific command. These variables allow you to customize the behavior of Windows PowerShell, variables such as VerbosePreference and ErrorView.
The default setting for variable VerbosePreference for example is SilentlyContinue.
For details of these variables and their default settings, see the Microsoft TechNet article about_Preference_Variables. (Applies To: Windows PowerShell 3.0). Windows PowerShell version 2.0 contains it’s own list also.