OK - I guess it's resolved, but I've got another related issue, I think - tell me whether I should start a new thread? I've set the Preferences on my new MacBook Air thusly:
Do not put the HD to sleep when possible (twice - in Battery tab and Power Adapter tab)
Do not enable Power Nap (twice - both tabs)
Prevent computer from sleeping automatically when display is off (I set display to go off in 1 minute when I'm not using the MBA)

So I expect the computer never to go to sleep - but I think it does anyway, because I noted the Progress percentage of tasks when I left the computer - then the display goes dark after a minute - I come back two hours later, and the percentage has barely moved, IOW it's moved only the amount that 1 minute took until the display went off.

So I think the computer is going to sleep despite my explicit instructions, and so it's not computing when I'm not using it. Is this a Mavericks thing? or a notebook thing? My iMac chugs along 24/7 and that's what I want the MBA to do, obviously, but it doesn't seem to be doing it.

???