@daxian-dbw - sorry to have just noticed this - the seemingly unnecessary try/catch statements did serve a useful purpose at one point. I recall hating adding them, but IIRC, it improved error reporting in some useful way. Sorry, but I don't remember more than that though.

Does it update ScriptStackTrace in errorrecord?

@lzybkr Thanks for bringing up that context. Looks like those try/catch were added only for functions that uses SteppablePipeline. Might it be related to errors thrown from within the steppable pipeline? I will play with it a bit to see if I can find out why.

The "better error reporting" might be related to PowerShell.AddScript(...).Invoke() doesn't throw on terminating error or exception, but instead keep the errors in the error stream.
Here is one example of that:

$ps = [powershell]::create()
$ps.AddScript(@'
 try {
     Get-Process -Invalid 42
 } catch {
     throw
 }
'@)
## try/catch/throw is needed for the exception to be thrown from $ps.invoke()
$ps.Invoke()

But it doesn't seem to be the exact reason for the try/catch/throw in the original mkdir and oss.
The following throws the exception even without the try/catch/throw in mkdir:

$ps = [powershell]::create()
$ps.AddScript("mkdir -Path blahhfe:\jkfjkjakfklajlkf -ea stop") > $null
$ps.Invoke()