Judging from the Intel website, that refers to "enhanced halt mode" (C1E, or something like that).
Intel mobile architectures such as the Intel® Pentium® M processor include Enhanced Intel SpeedStep® Technology to optimize power and performance according to the demand on the system. The technology operates by providing multi-point operating modes (referred to as P-State, P0 being highest CPU frequency) on the CPU that increments or decrements the processor frequency depending on the demand. When there is negligible demand on the system and the CPU is idling, it provides multiple processor sleep states (referred to as C-State; higher C-states such as C4 refers to deeper sleep state) that reduce the overall power consumption significantly.
Every interrupt will pull back the CPU from a deeper sleep state to C0 due to the interrupt handler that services the interrupts. This impacts the sleep state residencies that are critical to optimize the power consumed. There is also an energy cost associated in transitioning between multiple C-states. If the interrupt rates are high, the power savings due to deeper sleep states are negatively impacted due to the decrease in sleep state residencies and the cost associated with C-state transitions. While Intel® platforms offer platform-specific C3-like states, they require long residency (multiple milliseconds) to fully amortize their transitional costs. An aggressive interrupt rate can potentially negate the benefits of deep sleep states offered by the platform.
The closest AMD-based tech related to this is Cool and Quiet. Basically, if the processor is idle for a period of time, the computer shuts down the core to a specific degree. The longer the system is idle, the more the core is shut off. This saves power and in turn reduces noise.
The second paragraph basically answers whether you should use C-State or not. C-State is a personal choice. If the computer is only going to be idle for short periods of time, the paper states that more power can be saved by letting the core idle without entering C-State.
Basically, use C-State if it makes sense and you want to. If you use Cool and Quiet on your AMD machines, then you may want to use this too (Although this is a more intensive form of Cool and Quiet, because it actually shuts down parts of the core).
Isn't it amazing what questions Google can answer?