Piping lets you use the result of the previous command. This can shorten your scripts since it requires less text, and multiple commands can be written on a single line.
Example
Here is an example of piping, that shows a Get-List command for list "Documents" in a site collection:
$srcList = Connect-Site -Url "http://farm/sites/sitecollection" | Get-List -Name "Documents"Id : ab6a768d-3478-4302-8258-53f2c2637c12 Title : Documents BaseType : Document Library Source : /sites/sitecollection/ ContentApproval : False RootFolder : /sites/sitecollection/Documents/ EnableAttachments : False EnableVersioning : True EnableMinorVersions : True ForceCheckout : False Site : http://farm/sites/sitecollection/