I never let anything happen that I have not agreed to manually.

Updates, defrag,... happen ONLY when I have initiated the process, am am paying attention.  Updates are never allowed to be automatic.

Why: too many experiences of clients calling me to fix what was automatically accomplished over-night.

And I always install hardware updates separately, in case the need for rollback is required.
(Many examples of win updates installing bad vid drivers and printer fixes.)

Alternatively....

My Delta44 doesn't like sleep mode either. Either leave it on or turn it off. Besides you can use that time while you're sleeping to let the computer do its defrag, anti-virus scans, malware scans, and Carbonite backups. Just because you need sleep doesn't mean the computer does. 

Why do people leave their PCs on when not in use? What are the perceived benefits?

> What are the perceived benefits?

Might be hard to find the on button the next morning....

Why do people leave their PCs on when not in use? What are the perceived benefits?

Read my post above yours. Defrag, backup, antivirus, anti-malware scans can run instead of running while you're trying to use the computer, and if you're a charitable guy you can let the World Community Grid use your extra computing power during that time to cure Muscular Dystrophy, Childhood Cancer, AIDS, and more...

http://www.worldcommunitygrid.org/

... or downloading porn....  (scheduled of course).

I think the worldcommunintygrid is a great thing, but running a stable daw and being part of that are entirely incompatible.

I can understand leaving a machine on for a virus scan or backup that I've consciously decided to do, but leaving it on by default puzzles me.

"jm24"
At least a netbook should reside in the potty room.

Never, not here. Cell phones are also frowned upon. Ewww. A well stocked magazine rack is the best IMHO (National Geo., Sound on Sound, InTouch and the venerable Bathroom Reader). The InTouch mag. is great for little sessions of sudoku or the "Double Take" or the celebrity crossword. Keeps the mind nimble..., sort of. But the things I've learned with the "Bathroom Reader" are in some cases priceless but most of all darn funny (frivolous lawsuits and the likes) ...

"Bathroom Reader - Fluid Entertainment (excerpt)"
Q :: Do liquid crystal displays (LCDs) actually contain liquid?

A :: "In this case, the term 'liquid' refers to a peculiar quality of a certin type of crystal, not its physical appearance. The twisted nematic liquid crystal is the most common type used today. It has a naturally twisted crystalline structure. A particular feature of this crystal is that it reacts to electric currents in predictable ways - i.e., by untwisting to varying degrees depending on the current to which it is exposed. Hence the 'liquid' part of the crystal's moniker ...

And understandably, I never did check to see if they have an online presence (which I assume they do).