A developer on XDA website has written a guide/information page so we stop as soon as possible the discussions about how 8 cores are useless.
The Exynos Octa or Exynos 5410 is a big.LITTLE design engineered by ARM and is the first consumer implementation of this technology. Samsung was their lead partner in terms of bringing this to market first. Reneseas is the other current chip designer who has publicly announced a big.LITTLE design.
The point of the design is to meld the advantages of the A7 processor architectures, with its extreme power efficiency, with the A15 architecture, with extreme performance at a cost of power consumption. The A7 cores are slightly slower than an A9 equivalent, but using much less power. The A15 cores are in another ballpark in terms of performance but their power consumption is also extreme on this current manufacturing generation.
ARM's initial tests show that a big.LITTLE processor running in HMP mode is 10% faster than a big.LITTLE processor running in migration mode but with the same power efficiency.