Transgo Shift Kit Question, 727 Notch?

Hi all. General curiosity question here.... Just popped a Transgo shift kit in the 727 I have in the old Dodge. Tried searching around with no luck and am just curious what the notch you file into the valve body does? The kit was an easy install and the filing was easy and it's apparent Transgo has done their homework. I understand the concept of modifying the pressures with larger holes, valve changes and spring tensions, but can't come up with a theory for the notch. Any of you smart guys out there please feel free to educate me. Even though this forum doesn't apply to my make and model, I love all the drive-train tech I can find here and spend way more time here than anywhere else. Thanks!