When I have the choice/chance, I prefer to get this taken care of with the ticketing/operating airline before voluntarily not flying the booked flight. Even if the booked ticket has value after no-showing, if you wait long enough after a no-showing the PNR may become unusable and then the airline/ticketing agent has to go through and create a new PNR and affix the ticket to the new PNR/booking.

I've had some exceptions to the above kind of scenario, situations where I no-showed for the US-overseas part of very cheap roundtrip DL tickets but then another airline allowed me to use the return portion of the ticket as originally booked on the DL ticket. I was surprised by how reliably I was able to do OLCI for such situations a few years ago on the return part of DL tickets where I had no-showed on the first half of the ticketed booking. This of course wasn't how the ticketing and operating carriers wanted it to work on those DL tickets, but it turned out to fly anyway. I was shocked the first time it worked with OLCI but after that I realized it was definitely not a "once in a lifetime" situation but more like a glitch that takes place at time to time.