Should the layout group control the widths of the children?
If set to false, the layout group will only affect the positions of the children while leaving the widths untouched. The widths of the children can be set via the respective RectTransforms in this case.
If set to true, the widths of the children are automatically driven by the layout group according to their respective minimum, preferred, and flexible widths. This is useful if the widths of the children should change depending on how much space is available. In this case the width of each child cannot be set manually in the RectTransform, but the minimum, preferred and flexible width for each child can be controlled by adding a LayoutElement component to it.