You can very well use wall as a screen. Just make sure the paint is of good quality & closer shade of white and Matt. Else it will reflect hot spots. I am using it for many years without any refractions.
I preferred wall for 2 reasons,
We don't use PJ all the time. So I didn't want my living room wall to look differently by permanently fixing screen
There are no simply no wrinkles or curves for wall as compared go hanging screens from my friend 's. Also hanging screen may wobble a bit when you start fan.