I
always prewash. I notice that Craftsy recommend that you don't but I'm not going to put all that work in only to have it shrink or run after I've finished. I wash at 30°C as a matter of course.
I learnt that the hard way when I paid a king's ransom for floor length curtains only to have them swinging 4" up in the air after washing!
I took them back to be rehemmed and thereafter I washed my curtain fabrics and took them back to have them made up. The man in the shop laughed but since I was still spending squillions (removed window and replaced with French windows) he humoured me.
Having said all that I mostly make my own now.
In short...yes.