The problem with using broken parts as an "opportunity" to upgrade is the cost of recoveing the system.

It's bad enough having to take the time to re-install software but the real killer is having to negotiate with a dozen different companies and beg them to allow you to re-activate the software.

And I do back things up. But in the last series of failures I lost the PC itself, the file server with the data, and the system recovery failed for some obscure reason.

Bummer!

Most of the posts in this thread have thus far addressed physical factors of a system in the context of power cycles vs. perpetual running. But there can also be software issues or systemic dynamics to be considered as well, depending upon your OS and / or computing routines.

I never turn my system off unless I'm going to be away from it for a length of time beyond a few days. I work with it pretty much all day long, but then I keep it running all night as well for a few reasons.

I set it up to render lengthy projects on which I have been working. If my workflow necessitates it, I can spend my work day designing, cutting, and compositing my projects, and leave the lengthy render times for hours I don't have to be in the office.

Likewise, I will also set up the late night hours to perform batch compressions of projects. These are time consuming and I don't have to be present to make it happen.

The late night hours are also good times for various methods of system maintenance and regular backups. Again, much of this is automated. Since I use a Mac with the Unix core under OS X, it also runs those little automated maintenance sudo scripts - which I could override to run on command, but since I keep the system running through everything else, this is just a nice convenience I don't have to think about...and I find that due to these computing routines, my system runs quite smoothly and efficiently.

Maybe I'm being a little wasteful in the sense of energy consumption, but I feel that keeping a smooth running, well maintained system with an efficient computing workflow provides far more benefits in terms of productivity.

By contrast, I have a few friends who always power down their systems when not in use, and I am periodically asked to diagnose and treat their computers. Since their system is never optimized and their OS is never allowed to run its own background 'house-cleaning' tasks, I usually find tons of system errors, fragmentation, broken permissions and so forth. If I had to put a price on the time involved to restore the functionality and efficiency of these systems, and noting how the adoption of some computing habits could help make some of this effort avoidable, it puts the concept of 'wasteful' in a different light.

This is not to say that running through power cycles will cause havoc throughout the OS. I'm just suggesting that becoming aware of the needs and features of basic OS maintenance routines can also be determining factors for the 'when', 'how', and 'why' of powering down vs. perpetual computing.

-Jon