If you can't taste it, what qualities does it add to the Madras? I just figure that if you can't detect it, couldn't it be omitted?
Ahh, I was waiting for someone to say that!
I could give the example of using anchovies in certain sauces as giving the same effect, i.e. they're there, you know because you cooked it that they're there, and if you do it just right you can't really tell that it's anchovy you've added, but it improves the flavour of the dish. There are other examples too.
All I can say is that it 'rounds' the dish out in a way that, again in my opinion, improves it.