I used to explain it to clients as the difference between having your files nicely organized in cabinets or on shelves, and having the contents of several different files strewn over the desk. For people who like to keep a tidy desk this metaphor made immediate sense.
It explains some aspects and obscures some other ones.
It explains how the documents at arm reach on the desk are faster to access than the things in the cabinets. It obscures the fact that stuff on the desk dissapears if the power supply glitches even just a little.
In fact we invented these batteries with electronics which sense if the electricity is about to go out so the computer has time to carry the documents from the desk to the cabinets before they dissapear. And we think this is normal and even necessary in pro settings. (I’m talking about uninterrupted power supplies of course.)
A lot of people clear their desk before leaving the office, either because they're tidy and well organized or because they don't want to leave confidential info out where the cleaning staff could browse through it. It's not hard to extend the metaphor to a reboot of the computer being like the end of the workday.
