Veggie oil can get very gummy unless it has certain additives. As an IGH (internal gear hubs) user, the last thing I want in that hub is something that is going to gum up. I have had to tear down and clean more than one hub where the old 3 in 1 oil was used, it was gummed up so bad it would not work. In those hubs synthetics seem to be the best choice.
Aaron