It can divorce you from the reality of sex.
When you're having real, unscripted sex with an actual human being, things don't always go as planned. There's a considerable amount of fumbling, laughing, and "Hey! That's not my [anatomy of choice]." It's an imperfect art, at best. And that can be one the best—if not most human—parts of it.
It can be problematic if we bring our porn point of view (perfectly executed sex, every time) into reality if it translates to a lacking appreciation for what sex should really be—improvisation.