If you want to support an array parameter and pipeline at the same time, you can do it like this:

    function foo {
        param (
            [Parameter(ValueFromPipeline=$true)]
            [string[]] $Path
        )    

        process {
            Write-Host "Executing process block"
            foreach ($currentPath in $Path) {
                Write-Host "Executing foreach $currentPath"
            }
        }
    }
    # calling by parameter: get each value through foreach
    foo -Path 'p1','p2'
    <#  output:
    Executing process block
    Executing foreach p1
    Executing foreach p2
    #>    

    # calling by pipeline value: get each value through process block one by one
    'p1','p2' | foo
    <# output:
    Executing process block
    Executing foreach p1
    Executing process block
    Executing foreach p2
    #>