Why is remoting slower than running over the network?

temp.ps1

# Remote Code
  $SB = {
    param($file)
    $SHA1 = New-Object -TypeName System.Security.Cryptography.SHA1CryptoServiceProvider
    $stream = [System.io.file]::Open($file, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read)
    $hash = [System.BitConverter]::ToString($SHA1.ComputeHash($stream))
    $hash = $hash.replace('-','')
    $hash = "0x$hash"
    $stream.Close()
    return $hash 
    }

    if (-not(Get-PSSession -ComputerName $ComputerName)) {
    $CurrentSession = New-PSSession -ComputerName $ComputerName
    } else {
    $CurrentSession = Get-PSSession -ComputerName $ComputerName
    }

    $hash = Invoke-Command -Session $CurrentSession -ScriptBlock $SB -ArgumentList $file
# End Remote Code

# Local Code
			$SHA1 = New-Object -TypeName System.Security.Cryptography.SHA1CryptoServiceProvider
			$stream = [System.io.file]::Open($file, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read)
			$hash = [System.BitConverter]::ToString($SHA1.ComputeHash($stream))
			$hash = $hash.replace('-','')
			$hash = "0x$hash"
			$stream.Close()
# End Local Code