C1E is a power management state that allows the processor to reduce power beyond just the cores. With C1E, the processor power can be reduced by lowering the memory controller clock speed and halting the HyperTransport™ technology links.

C1E is a power saving feature for the CPU, when your PC is idle it will drop the frequency and voltage, reducing power usage and heat.

CPU Enhanced Halt (C1E) : A power saving feature in Intel chips, enabling C1E will allow the operating system to send a halt command to the CPU when inactive. This halt state reduces both the processor's voltage and multiplier so that it consumes less power and runs cooler.

C1E Also known as enhanced halt state C1E is also a power saving feature and when enabled will allow your CPU to switch to the Minimum Enhanced Intel SpeedStep Technology operating point, when all execution cores enter MWAIT (C1). In some cases disabling this feature can improve CPU latency.

C1e is an enhanced power state used by processors and not required by the apci standard. Basically the cpu just halts (stops processing) but can wake up when needed to resume.