I have the Weathertech sunshades...
I have the full set, but I don't use the rears since I have the OEM shades for back there. All of the shades fit very well. They even stay in place when I roll down the windows!
And the car stays much cooler on hot days.
Privacy. Some know that I have "some electronics" in my car.
Although sun shades are no guarantee against theft, having them up any time the car is parked means people are less likely to see what's inside and feel compelled to break-in. Again, not a guarantee; just a little bit of concealment. I remove the desk and computers when I don't expect to use them for a while. But the radios are always in the car unless I'm staying overnight away from home.