Why you need a windshield sunshade during an expedition
1. To protect your vital electronic devices: Off-road driving in remote areas is a risky lifestyle that will turn even more dangerous in case of GPS or communication device failure. Exposing your cb radio, ham radio, satellite phone, or gps backroad mapbook to high temperatures and/or sun rays is a good way to get yourself in trouble. Even a quality personal locator beacon is not invulnerable.
2. To sleep in your Jeep: As my followers already know, I'm sleeping in my Jeep most of the time (How to sleep in a JK 2-Door) because it's more productive. I'm constantly on the go for my work and need to drive at night often. So, I'm used to sleep in my Wrangler JK during the day. But even if you don't intend to sleep in your vehicle at all, that will happen anyway for the following reasons: 1) You won't be able to pitch a tent all the time (heavy bear territory, camping is forbidden, bad weather, etc.). 2) You'll be too tired to pitch a tent. 3) You'll just need a nap during the day. For all those reasons, having a windshield sunshade might improve your sleep. As a solo off-roader, you must know that fatigue is your first enemy. If you are too tired to think, your situation might go downhill in a minute. If you get stuck somewhere, sometimes it's better to take some rest instead of making a poor decision (and damaging some drivetrain parts or components, for instance).
3. To extend the "shelf" life of food supplies: Unless you want to have kidney stones or other serious health problems, you will avoid sodium-rich and canned foods on the trail. Of course, you can rely on high quality freeze-dried meals for a while (Alpine Aire, Mary Jane Farms, Backpacker's Pantry, etc.) but it's expensive as hell (figure 50$/day for a grown-up man). The cheapest way is to eat (mostly) fresh fruits, veggies, bread, etc. Turning your Jeep into an oven decreases the shelf life of those valuable food supplies. When should you use the sunshade? During long trail repairs and/or recovery operations. Or just when you stop somewhere for several hours because you want to enjoy the outdoors (taking pictures, swimming, fishing, hunting, wildlife watching, etc.). Don't forget to park your Jeep facing the sun.