Dan,
While glassing sunlit hillsides for the reason you state holds some water, the main reason to do so is two-fold.
First, the sun isn't shinning into your binocs or spotting scope. Second, the sun on the hillside makes it easier to spot deer, especially if they are bedded. Often, the only hint a deer is there is the sunlight glinting off an antler.
Here's the section in the HOW TO HUNT COUES DEER book that sorta covers it:
Duwane has honed his glassing skill into an art and often jokes about his method. "I spend so much time in the woods, I can get worn out covering several miles every day. Besides, most of my hunters would die if they had to climb up and down the hills all day.?
?So for many years now, I've let my eyes do the walking and call it my ?three B? method. The first two Bs represent my binoculars and backside. The last stands for the brains for figuring out how to use the first two,? he said.
If Duwane hasn't hunted an area before, he likes to scout it prior to the season and locate several possible glassing spots overlooking prime whitetail hangouts. Sometimes those places will be small, isolated basins, and at other times it might be a mile-long canyon with a wide-sweeping panorama of a ridge.
Deer are easier to spot when they're moving early or late, but glassing is an excellent way to spot bedded bucks any time of day, as well. If you do find a bedded buck, the stalk is frequently easier than going after one that's feeding because the bedded deer normally stays in one place for while.
One key aspect to good glassing is patience, according to Duwane. ?Too many guys try to cover the terrain quickly and probably miss more deer than they see. Just slow down. Every time you move that tripod head, spend at least five to 10 minutes picking the new view apart. Thoroughly search under and behind every tree and investigate anything that remotely resembles a deer or a part of deer. Especially keep your eyes open for the sun glinting off an object; it could be horns or a deer?s back,? he said.
Devising a consistent system is a good idea, too. If Duwane is glassing a ridge, he starts at the top and either at the right or left end. Once he completely checks his first view, he pans the tripod head just far enough to get a new view that slightly overlaps the area he had just looked at. He continues doing the same thing until he reaches the opposite end of the ridge from the one he started at. Then it's time to vertically lower the binoculars a tad so the very top of the field of view overlaps the first horizontal zone by a bit. He then repeats the panning process across the length of the ridge. By making multiple horizontal passes, he eventually makes his way from top to the bottom. Then he does it again.
Focus is another critical factor. Depending on the distance to the area you're glassing and the power of your binoculars, you might have to refocus quite a bit to compensate for the slope angle as you move from the top to the bottom. This holds especially true with high-power binoculars and short distances.
Duwane suggests glassing slopes that face south, east and southeast early in the day, then switching to the north, west and northwest slopes later on. That way the sun isn't shinning into your binoculars. Instead, the sunlight hits the area you're glassing.
TONY MANDILE
How To Hunt Coues Deer