vCenter Server ships out of the box a number of system and custom roles, which can be used or users can create their own custom roles containing the required privileges. If you wanted to understand which roles are actively being used, the following PowerCLI snippet can help provide insights to roles that have been assigned. Furthermore, the script will also output to a file, that contains all he privileges defined for the vCenter Roles that are in active use.

$roles = Get-VIRole
$permissions = Get-VIPermission

$results = @{}
foreach ($permission in $permissions) {
    $role = $permission.Role
    if($results.ContainsKey($role)) {
        $results[$role]+=1
    } else {
        $results[$role]=1
    }
}

Write-Host "`nTotal Roles: $($roles.count)"
Write-Host "Total Roles Used: $($results.count)"
Write-Host "Role Usage:"

$results.GetEnumerator() | Sort-Object -Property Value -Descending

$outfile = "used-roles.txt"
foreach ($key in $results.keys) {
    $role = Get-VIRole $key
    if(!$role.IsSystem) {
        $key | Out-File -Append -LiteralPath $outfile
        "=========================================================" | Out-File -Append -FilePath $outfile
        $role.ExtensionData.Privilege | Out-File -Append -LiteralPath $outfile
        "" | Out-File -Append -LiteralPath $outfile
    }
}

Here is an example output of running the script:

Here is an example output from used-roles.txt file that is generated, which contains the list of privileges for each role that is in use: