As the title says, it is easy to see the effect of the margin when using regular unwrap or doing a Lightmap Pack, but it barely has any effect when you crank it up to 1 with Smart UV Project.
I see a significant effect with a demo object (unwrapped with Smart UV Project)
Show us what you mean
i attached the blend file and the pictures below show the difference between 0 and 1. thanks for looking
lavatory.blend (1.72 MB)