Originally Posted by Sheldon Brown
Modern cables and housings generally should not be lubricated. The viscosity of the lube actually gums up the works. The exception is where the shift cables run through the guide under the bottom bracket. A bit of grease there now and then is a good thing.
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I put new cables and casings on a Moustache handlebar with barcon shifters and there was too much drag through the long casings with twists and turns. That white grease in the spray can made shifting slick, smooth, and easy.