Less people would equal...more gas all around, more jobs to go around, less expensive healthcare, better health overall, less crime, better quality of life for all, less wasted raw materials, better for the environment, more space per person...the list goes on and on... better illustrated below.
It would mean more gas to go around because their would be less demand (cheaper gas)
More jobs because we could free up 12 - 15 million lobs just by getting rid of the illegals.
Better healthcare because the healthcare system wouldn't be flooded.
Better health overall because anytime you get too many individuals in a small area...you get sickness. (mother natures population control)
Less crime because its proven that crime is lower in less populated areas...even if you measure it by %.
Better quality of life because...well... just because it would be better.
I don't have time right to finish explaining....but I'm sure you get the idea.