The answer to that is "it depends". It depends if you use Isotalic resin, lay up resin, etc... some resins actually will never cure, giving the warped looked after a few years. I personally experienced this in laying FG Lamborghini Countach kit cars in the 90's.
But with the micro sphere balls, it will make it light weight and increase the strenghth, but as Combatbaby has said, the rotocast will actually make it heavier. FG outershell allows people use bondo easier on the outer surface.
Shoulders next for bro while sculpting the face, waiting on Fedex for my KLAY.