Power saving in Multi core.

Dear All, We are using ARM cortex a9. In below scenario, I want help. Multi-Core Power Saving Hot plug feature allows for making a processor offline and let the system run as if there is only a single core. Now,comes the scenario - Let there are '2' cores in the system both running at a load of 40% (i.e. total load 80%), now in this case ideally '1' CPU is sufficient. So, if we make 2nd Core offline that will make the system execute everything on core '1'. But will there be any power saving if we make any core offline under scenarios like this? Or will this have extra overhead? What are the pros and cons of working like this on Multi-Core? Regards Naveen