Never. Lubrication always helps guide it and glide it, and I'm thick enough that friction without a lot of lube is just painful for both of us.
I also just fucking adore the visual of a wet pussy leaving a few drops of dew, and getting wetness and grool all over myself. They may not be able to produce semen and cum on my face, but getting the stickiness all up in my cheeks and beard when going down on her is the next closest thing.