This partner pose helps the student develop and feel the back strength necessary to hold arms in front. It also helps the standing partner to see how the sacrum tends toward lifting and moving up or down as the student in warrior 3 raises the back leg. Its a good visual to see it on another person.
Standing partner doesn’t grab arm or hand of Warrior 3 partner. She is just there as a support. Standing partner can give feedback as to the levelness of warrior 3 sacrum position.
Next step is the standing partner allows one hand to release from the posture so the Warrior 3 has to use more back and core strength to remain in good alignment.
If the warrior 3 student wants the standing partner to release with no support – she can communicate that desire.