A short table of values (see below) tells the story in a pretty interesting fashion. I let three different Vista notebooks run at idle and then put them to work defragmenting their system drives (using the excellent Raxco PerfectDisk 10 beta product, which I’m also currently working with right now) using all three of their predefined power regimes (called power schemes prior to Vista’s introduction, called power plans inside Vista today; see this MS Help FAQ on Power Plans for more info):

• Power Saver:
  Saves power by reducing system performance, to help notebook PC users maximize battery life (also results in cooler operating temperatures).
• Balanced:
  Saves some power by reducing system performance while systems are idle, but also boosts capability (and power consumption plus heat output) during peak demand periods.
• High Performance:
  Maximizes system performance and responsiveness, resulting in shortened battery life and higher operating temperatures.

Notebook-Idle    PS    Bal    HiP
Dell D620      25-27  25-41  25-53
Acer 8920G     32-36  35-38  36-40
HP HDX 18      35-37  35-38  36-47

Notebook-Defrag  PS    Bal    HiP
Dell D620      25-46  27-57  27-65
Acer 8920G     32-40  35-45  36-46
HP HDX 18      35-41  35-43  36-47
Note: PS = Power Saver, Bal = Balanced, HiP = High Performance, 
all temperatures are in degrees Centigrade (° C).

What’s interesting about the data in this table is that the temperatures run more or less the same for these power plans whether or not they’re plugged into a wall socket or running off battery. What this tells me is that enterprises can save money on hardware by extending its life with cooler-running power plans, to a much greater degree than might immediately seem possible. Though results do vary as the Table data shows, it’s also the case that using the Power Saver on the road/untethered, and the Balanced plan in the office/plugged-in, and High Performance never will save wear and tear on notebook PCs and let companies use them for a while longer than they may have expected them to last. Sure, they’ll also save a little on power as well, but I’d expect to see the savings on equipment overshadow those numbers significantly. The question then becomes: Will the users go along with this approach? I didn’t notice much performance difference between Balanced and High Performance, but the step down to Power Saver caused the GUI to run noticeably (though not painfully) slower.