how does torching the oil serve military purpose? Oh, turning day into night, making it so night vision can not work correctly, put the oppisition into as much discomfort as possible, mind games, many different things. I am not saying it is right or a choice I would make, of course I am not facing the allies either so I can not say for sure what I would do, but it does have it's function's on a military position...
Same as using Agent Orange and defoliation in jungles, or 20,000 pound plus conventional bombs, or cluster bombs, mines, flame throwers, cannons, all the chemical and bio weapons we the USA have in storage, many different things that seem so mindless, have a purpose in war...
just my pov...