First, it depends on your weight. Second, it depends on the texture, shape and suitability of the chair. If you put your feet on the bar under the stool, your legs will unconsciously form eight rows, which is not conducive to a young person, especially primary and secondary school students, and it is easy to cause bone deformation. Putting a tripod up will also form a habit of shaking your legs. As we all know, shaking your legs and crossing your legs easily lead to short legs, different thicknesses of legs, or even more serious. If you form a habit, it will be more difficult to get rid of it. The function of the crossbar is to hold the stool legs and prevent them from cracking.
The bench is under the downward pressure of people or things, or under its own gravity. This force is borne by two legs. Let's analyze the stress on the splayed leg. Its upper end receives vertical downward pressure and its lower end receives vertical upward support from the ground, so its left leg receives clockwise torque. Therefore, if the cross brace in the middle is close to the table, it will be horizontally pressed to the middle. If the middle cross brace is close to the ground, it will be pulled horizontally to the middle.