I note that the instructions that came with the carbide dies for my friend's 500 Smith suggest that use of a lubricant, while not necessary is recommended.
It does make sizing easier, especially on that large case. On smaller cases the reduction in force may be less, but still, as others have said, is noticable.
Remember to clean it off. Contaminating your powder is only one of the evils stray lubricant might cause. Sticking in your chamber would be problematic, too.
Do not use too much. I have been told that lubricant that gets up behind the carbide ring that is pressed into the die might let the carbide ring slip out.
All in all, for the decrease in sizing force and longevity of your brass and your dies, it seems worth the small risk and trouble. What keeps me from doing it is the cleanup, which would interrupt the cycling of my brass (I use a continuous mode.) If you load in batch mode, that would be much easier to incorporate lubing your cases into the process.
Lost Sheep