Interesting to see people mention having them on their target rifle but not their hunting rifle. For me I can see it used in the field because hunting is usually done when the sun is low in the sky. When I shoot matches 9 out of 10 people do not use sunshades. No, I haven't counted but that seems reasonable from what I've saw.
Very few ranges are set up with the morning sun in your face, if it is they were very limited on options or it was not very thought out. I've personally never shot a match where the sun was an issue.
For the record, the sun sets in the west. The wind in hunting season comes from the north west. If you pay enough attention to the wind you will be looking close to the sun every evening.