If my layer is rasterized and I select something (say with the marquees ellipse), the filters apply only to that selection - moreover - they apply centered on the selection.
For example, using the Spherize filter on rasterized layer with a portion selected with the marquees ellipse, then the center of the sphere would be the center of the ellipse made with the marquees.
If my layer is a smart object, it doesn't work this way. All filters are centered on the entire layer.
For the sake of avoiding the xy problem, here's what I'm trying to do: A have a text layer wherein I want the text to look like it's going to burst open like a balloon. So I want to select some of the text to spherize so it looks like it's bursting or blowing up.