Especially in Bleak Falls Barrow,

Oil seems to be conveniently spilled in not so great areas. And the enemies seem to make no mind of it.

It's there for the player to use the environment to their advantage. Like say, an explosive barrel. A concept that has been in video games for some time. It's doubtful convenience matters very to me so long as I can use it strategically in gameplay.

Yeah, its more for gameplay. Though I tend to burn it off beforehand so it doesnt get accidentally tripped and toast me.