Because the name says rest angle you cannot arrive at simple features. Although there are only some features mentioned here
Can be helpful for back pain
A wedge pillow can provide just enough of an elevation to stack the hips and vertebrae in the ideal spinal alignment in persons with certain types of back discomfort. People who suffer from upper back discomfort usually benefit more from a wedge cushion than those who suffer from lower back pain.
Nighttime asthma cure
A wedge cushion protects patients with nocturnal asthma from the negative effects of gravity by preventing blood from accumulating in the lungs, which can be one of the reasons for breathing problems.