A couple of quick functions for AD group maintenance

Clear-ADGroupMember.ps1

# requires version 3.0
<# Clear-ADGroupMember
.Synopsis
   Removes all users from an AD group
.DESCRIPTION
   Removes all users from an AD group provided to the script.
.EXAMPLE
   “my-group” | Clear-ADGroupMember

#>
function Clear-ADGroupMember {
    [CmdletBinding()]
    #[OutputType([Microsoft.ActiveDirectory.Management.ADGroup])]
    Param(
        # Identity of Group to depopulate
        [Parameter(Mandatory=$true,
                   ValueFromPipelineByPropertyName=$true,
                   Position=0)]
        $Identity
    )
    Begin
    {
    }
    Process
    {
        $ExistingGroup = Get-ADGroupMember $Identity
        Remove-ADGroupMember -Identity $Identity -Members $ExistingGroup
    }
    End
    {
    }
} # End Function Clear-ADGroupMember

Get-UnusedGroup.ps1

Function Get-UnusedGroup { 
  [CmdletBinding()] 
  Param( 
    [Parameter(Mandatory = $True)] 
    [string]
    $searchBase 
  ) 
  Get-ADGroup -Filter * -Properties members, isCriticalSystemObject -SearchBase $searchBase |  
  Where-Object { ($_.members.count -eq 0 -AND !($_.IsCriticalSystemObject) -AND $_.DistinguishedName -notMatch 'Exchange Security' -AND $_.DistinguishedName -notMatch 'Dns') } 
  $searchBase = $null 
} #end function Get-UnusedGroup