Thanks for the input.
I was wondering about that raw extra data because comparing the file size of the incremental with the final it is always double, so if there is extra data then it make seance.
I am just using the incremental as a learning method for now, trying to figure out renderings time and comparing mostly with V-Ray, so see who clean first.
I am still new to this progressive method to I am trying o find a way to predict in some way how long I need to coock the images to be acceptable. At the beginning I though it was based in passes, like I need 100 passes for an 3000 pix image to be clean, but now I am not sure, let say I have to have 3 images done in one machine, how to know how much to cook. V_Ray give an estimation that is a good reference, with progressive, hard to know.
Thank again.