The Frog Stretch assists us in keep the hips from internally rotating with squatting motion.
Skip to the 2:23 mark here for a video demonstration.
I would use this with people who actually have passive range of motion restrictions not allowing them to get into a proper squat.
I wouldn't use it for people who knees cave their knees from purely lack of form.
For those people, I would use the Quad Rock drill or add more trunk stabilization to their program.
Stack the shins under the knees. Keep a long spine
Don't over do this one! A little goes a long way.