Of course not. No interpolation means full calculation. Once you check the box, larger parts of the GI and IL are going to be 'guessed by interpolation' by Carrara. The higher the number of the interpolation slider, the higher the precision, because more calculation will be done. Perfectly logical. Interpolation is a lower-quality and faster way of calculation (not unlike the jpg compression method that describes larger samples of information is) and you give up some quality for increased render speed. Not using any compression/dergrading is always better, but most of these are created to save time and/or space. --- But it seems every answer you get on your questions and remarks will bring you the conclusion that either Carrara or Eovia suck big time (and your brilliant mind has come up with far more superior solutions). If you want to spend your days shaking your head over the dumbness of the rest of the world, that's fine, but on me you do not make a very smart impression. Trying to find things out for yourself (make some test renders with different settings to compare them) is not that hard. That is called 'learning', that does not have to be taken care of by anyone else but yourself.