I always agreed with this until.....
A couple nights ago I'm working at my favorite complex. Turf, close to home, good host organization, all that. Anyway, field 2 gets real nasty when the sun sets, moving from the left field corner all the way into left center and then FINALLY disappearing. Using my new Champro magnesium, thanks to @rjdakin, I actually had enough separation between my hat and the frame to where I could see over the top bar a bit. The sun was coming in right through the slits above that top eye bar and I caught myself thinking, "Man, a sun shield would be awesome right about now."