When I was an engineer for facilities at North Slope Alaska, the Alpine and other far western fields had to do this even for the pipeline transport. We had a very light oil from that location and the vapor pressure was causing problems is a system originally designed for far lower.
I imagine that this process has to be done at the refinery anyway? Although I suppose doing it at the end is most cost-efficent - but I guess this just means some of the refining process is moved closer to the oil fields? (More jobs for North Dakota!).
Does it also reduce the volume of the load being shipped? I would imagine it does, so more usuable oil can be hauled in each tanker car.
Would this process produce some usable products that could be sold? It almost sounds a little like a refinery operation.