It's purely based on fantasy. I guess that for people who don't have strong requirements for someone's physical corporality (not sure if that is the right word 😀) it might not pose as such a big problem but I realized that I should never sext again. What I want to say is that if you never met the person you have to use your previous experiences or your imagination to fill the gaps that you can't know through the screen. If you don't intend to meet, I guess it could work just to live some small fantasy but if you build some kind of attachment and would like to meet then what? You might find out there's in fact zero chemistry and you're going to face the person you wrote all those things to which were just pure fantasy and ooops, the fantasy doesn't match the reality. So it all were just lies.
Sharing nudes. Nope. I've never done that, never will and don't understand that.