[Byte[]]$Value = [System.IO.File]::ReadAllBytes('C:\Some10MBfile')

#  ~1000ms for 10MB array
#  ~0.5ms for 1byte array
function MandType {
    Param (
        [parameter(Mandatory=$True)]
        [Byte[]]$Value
    )
}

#  ~0.3ms for 10MB array
function TypeOnly {
    Param (
        [parameter()]
        [Byte[]]$Value
    )
}

#  ~0.3 for 10MB array
function MandOnly {
    Param (
        [parameter(Mandatory=$True)]
        $Value
    )
}

(Measure-Command { MandType $Value}).TotalMilliseconds
(Measure-Command { MandType ([Byte[]]@(0))}).TotalMilliseconds
(Measure-Command { TypeOnly $Value}).TotalMilliseconds
(Measure-Command { MandOnly $Value}).TotalMilliseconds

PS C:\> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.0.0-beta.9
PSEdition                      Core
GitCommitId                    v6.0.0-beta.9
OS                             Microsoft Windows 10.0.16299
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0


PS C:\> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.16299.19
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.16299.19
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1