Answer: The Analog Power parameter sets the power at which the internal reference generator operates and also sets the power to the SC blocks of the device. Below is the excerpt from the Technical Reference Manual from the Analog reference section.
The reference array supplies voltage to all blocks and current to the Switched Capacitor blocks. At higher block clock rates, there is increased reference current demand; the reference power should be set equal to the highest power level of the analog blocks used.
So, for example, if you have a PGA operating at Medium power and another Comparator operating at High Power, the Reference power should be set to Ref High. Also, if you have any analog resource that occupies an SC Block (like ADC, DAC, Filters etc), the Reference power should be set to "SC On / Ref xxx". If the reference is set to "SC Off / Ref xxx", the analog resources placed in the SC Blocks will not work.