It appears that the chip manages the power states itself. Again getting exact information on this is a pain and I'm really surprised (well maybe not so surprised) that Apple hasn't said anything about this. You'd think if they make such a drastic change to the system and to the Energy Savings pane of System Preferences there would be something.
From http://www.itpro.co.uk/desktop-hardware/19655/intel-haswell-release-date-and-spe cs-revealed#ixzz2iJsWa73p
Haswell chips will have 3 power states, compared to two in its predecessor, Ivy Bridge. These will be Active, Sleep, and Active Idle. Intel claims the advanced power saving will help give it at least 20x power consumption improvement over third generation chips.
It appears that the CPU will put itself to sleep if it is inactive for so many cycles. In a way this makes sense, the old method of telling the system to sleep after so many minutes is really very imprecise.
The only reason not to put the system to sleep as soon as it is idle is that it takes some amount of time to wake-up. So the lag would be annoying if it happened each time the system was idle. With the Haswell chip (as near as I can make out) wake-up is almost instantaneous. So there is no lag going from sleep to running. With no lag then it becomes feasible to put the CPU to sleep sooner and more often.
Again there is nothing I can point you to that states this it's what I've pieced together from various sources. In any case the missing setting in System Preferences is not an error so I guess you'll get to experience fist hand how this all works. Post back with your observations, it will be interesting to hear what you think.
regards