The usage of the Automatic Tee Insertion function is as the title suggest automatic. Every time two branches are connected, that usually involves one branch that is dragged (either an end point of it or the branch as a whole) and one that is stationary. When the dragged branch is released the Tee shape specified in the Diagrams Options is dropped over the stationary branch with the branching connector pointing towards the dragged branch. The dropped Tee splits the stationary branch as if the Tee was dropped by the user and the branching connector of the Tee is connected to the dragged branch. Thus completing the process of connecting two branches with a Tee.