Experiments on soil compaction show the rolling to be better, the roll needs not to be that heavy, only to kill the vegetable. Also, you don't do a separate pass on the ground, you just roll it at sow time, so no extra gas. Also, the vegetable cover absorbs CO2 and later fix it to the ground. Here is a thorough comparison of soils and methods https://www.youtube.com/watch?v=uUmIdq0D6-A