DirectGui positioning Button in Frame

I am a bit confused about frame center and origin.
Usually in gui frameworks, things are a bit more simple, I think normally is when I modify the appearance of a property that changes its look, the change should propagate to all other properties that in sum have same effect. Why I would want to change the button’s origin ?? Or I missed something, maybe its usefull when you have complex polygon shaped Frames. Thanks for you help.