The oil from a 'good' base will provide one chef's spoon per curry all night long, until the base itself runs out. Watch the malik's videos if you don't believe me.
Using the oil from the bunjara is an option but not a normal procedure I would conjecture. It's an Ashoka thing and nothing more.
If you really want to experience the true POWER of reused oil then add extra oil while making your curry (feel free to chip in anytime CQ) and recover this. Then use this on your next curry. It is not what the BIRs do but it is so good that you'll never look back. I'm guessing that in its small way it replicates what the BIRs do on a larger scale.
Try it!