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:
# Connect to the SharePoint site and retrieve the "Documents" list
$srcList = Connect-Site -Url "http://farm/sites/sitecollection" | Get-List -Name "Documents"
# List properties of the retrieved "Documents" list
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/