We have all been in that burning squatting position, whether it be gym class, exercise, or using a public restroom.
The question is though, is it an effective exercise, or can my time be better served?
The truth is...different strokes for different folks! If you are trying to lose weight, tone up, or add mass, then you are wasting your time!
Isometric exercises, improve muscle in only the short range that you hold the position, they do not burn a lot of calories, and in the case of the wall squat you take the core out of function to isolate the quadriceps and gluteal muscles.
For goals of losing weight, and toning up; you are best using compound functional exercises, and if you are coordinated enough, use a speedy tempo to maximize muscle fatigue and calorie burn.
For instance, instead of a wall squat you can try Barre squats with little bounces sinking deeper and deeper until your thighs get parallel to the floor then jump, and start over.
That being said there is benefit in isometric exercises, such as: less repetitive joint stress, post surgery, recovering from an injury, correcting posture, joint stabilization, and helping develop the mental toughness to push through the burn (which can help to raise the intensity in all other exercises).
There can be some functional training to it, such as some sports that require extended time in a semi squatted position: skiing, baseball, volleyball, etc. or if you find yourself routinely using public restrooms!