I dunno Chris, personally it's unlikely I'll ever use it - considering how well the image cleans up using noise reduction plugins.
I just hate waiting around for the ICNR frame to complete - especially if it was a 30 minute exposure
I'm very impatient.
If you had multiple shots of a few minutes each, then perhaps taking your own manual dark-frame would be better, because you'd be able to apply it to all of your images (assuming the settings were the same).