Gist
They can build bracing endurance if the trunk is held deliberately, but the wall removes much of the balance demand found in unsupported squats.
The calves contribute to foot and ankle stability, but wall sits do not include the repeated plantar flexion needed for a strong calf-growth stimulus.
They involve the hamstrings isometrically, but the growth stimulus is usually small because the exercise is dominated by knee-extension demand.
Yes, mainly for isometric strength and local endurance. They can contribute to quad growth if progressively overloaded, but dynamic training covers more joint angles.
Only to a limited degree. The glutes help hold the position, but ordinary wall sits usually provide less hip-extension loading than dynamic squats or hinges.