I think a popular use would be to allow the timestamp to only display if it has changed since the last message. For instance I often see scripted themes use timestamps which will display something like:
<joe> hi
<mary> hi joe
<joe> what's up?
<mary> not much, you?

Using a custom identifier it could be as simple as
alias mytimestamp {
  if (%last_ts == $asctime(hh:nntt)) return
  else {
    %last_ts = $asctime(hh:nntt)
    return $asctime(hh:nntt) $+ $crlf

That would be assuming that $crlf worked as a newline, but anyway, I'm guessing this is the kind of thing people would use it for.

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