Why (OR) Under what circumstances should I use the 'Flip Shell Elements' command while I mesh surface or sheetmetal parts.

I know grey surface is top surface and default orange surface is bottom surcae and solidworks meshes the center of the part.

But my question is ........does the top surface (grey color) always be the load bearing surface or does it always have to be tensile surface? What is the definition of top surface if there is any?

When should a surface be a bottom surface? Can bottom surface (ornage) be the load bearing surface? or should it always be the surface opposite to the load bearing surface?

Is there any clear brief explaination as to which surface should be top and which should be bottom for a particular part? or does it depend on part geometry, Boundary conditions or someting else?

Am I missing something here? Does the top and bottom matter as long as the mesh is aligned?

Thank you