Im glad you asked this question because i was thinking the same, would love to know the answer too as im not a fan of filing and im still a little confussed about pop its.
Great work carl btw.
well in this case the cuticle area is the most fragile (as it's basically just a fraction tougher than skin) and it also happens to be the area that i dont have to file, if you watch the video.
check out other popit/dual system form videos/threads and you will see there is minimal filing.