I've had 3 truck campers and only 1 had an awning, a side one, and I only used it once, just because it was there.
Everywhere we camp at, seems to have very high winds kick up, unexpectedly, on a regular basis, which destroy fabric awnings quickly. So many times out at the desert, I've seen folks put out their awning, then later go for a ride. The wind kicks up while they're gone and they come back to a torn up awning. So, I don't use them.
I would probly use an awning once in a while, if there were any made much heavier duty, such as like one of those sliding metal truck bed covers that rolls up like a commercial garage door. I think those would last alot longer in high winds than a fabric awning.
I also agree, a truck camper on a 4wd truck, the roof is really high up there and also the awning is not very long, usually 8-10', depending on length of camper. Because of it's small size and high mounting height, the awning is useless for much shade or rain protection, especially if there is any wind with that rain.
If the awning were mounted at the height of the bottom edge of the overcab bed area, and ran the full length of the camper, from the rear all the way to front end of the overcab bed area, then the awning would be a much more useful length and height for providing shade and rain protection.