Doctors and physiotherapists strongly recommend the use of the support cushion because of its ergonomic advantages.
"Research done during the recent years on discomfort experienced and even injuries sustained by guitarists has placed the blame on the commonly used footstool. The footstool produces an oblique twisting of the pelvis resulting in an S-shaped bend in the spinal column, a displacement at the base of the neck of the 5th, 6th, and 7th vertebrae, placing strain on the nerves leading to the arms, thereby hindering the guitarist. Many guitarists have regretfully experienced this through permanent injury done to their arms and hands, leading to cramping and even paralysis of their fingers, forcing them to give up their activities as guitarists. To prevent this, the footstool may be replaced by a guitar support or cushion above the knee, under the guitar. Use of a cushion had proven to be a singular factor in the elimination of the problems caused by the footstool. Therefore I advise all guitarists who use a footstool to adopt, instead, the cushion." (signed) Dr. Lennart Silverstolpe M. D.
Dr. Silverstolpe had conducted extensive research into the fatigue, discomfort and injuries suffered by professional musicians and music students.