In a preliminary design, the thickness of a slab has not yet been calculated, so we choose a slab style with an approximate thickness.
For implementation plans , the thickness often changes so we have to make an new slab style and substitude. And then we have to adapt the levels because of gaps or overlaps at wall heights.
Wouldn’t it be a lot easier if the thickness of the slab is determined by levels (Top of Structure an Bottom of Structure). A change in slab thickness would be a simple change in the level set-up and all other objects like walls would follow this change automatically.
There is another advantage to this : we don’t need a slab style for every possible slab thickness.