This software really needs an option to have the infill intelligently form only in areas it is required. This would save so much time and material on really large prints. I attached an image to show exactly what I mean.
The infill should be able to slowly form on an interior wall, to meet up to the above surface. If you are printing something 20 inches tall you do not need that much infill... If you make thicker outer walls the only thing infill is for is to be used as a platform for large flat areas to lay down when you get to the top. This should be a must add feature!
The same concept could also be used for support for overhangs that are really high up in the model.
What do you think?