Inverse kinematics (IK) is used to position things precisely.
Because Spine (like most realtime/game skeletal animation systems) uses continuous time and not discrete frames, it's not enough to go through every "frame" in Spine and align the foot with the floor. There is a virtually infinite number of points in time that the game update timespan can land between the "frames".
You either have to use IK or cheat the animation or the structure somehow.
