Why exactly would you use gradual infill?

[a-burke 0]

I understand that gradual infill helps to save material by using less at the bottom, but why specifically does it use less material at the BOTTOM, when wouldn't it make much more sense to use less material at the TOP, allowing the denser bottom to provide more support? Is there a benefit to having most of the material and mass at the top of the print?

[nallath 1,124]

If you have flat top surfaces, those are the areas that you want supported by infill. Otherwise you might get sagging areas. The bottom generally doesn't need this as it's printed on the bed.