I keep all my used oils, i have cheap Chinese chainsaws that i use it in for chain lube and also a few drops mixed with kerosene on a rag to help light the furnace/incinerator.
I do remember using it with Creosote some years ago but i think Creosote is banned in most Australian states now. I think it may be toxic. My old timber house has creosote & oil mix on the stumps and i never seem to have any problems with termites, great stuff.
Someone on here created a workshop heater from an old paraffin fire, drip fed with used oil from an elevated tank. Cant remember the post though but it was a pretty cool project.