Beekissed, if I could give you 3 reasons, would that help?
1 ~ Alleviates boredom. Sometimes you're the only one around, or it's late, or you are just finished with other things.
2 ~ Helps clear the mind, and let's you "re-set." This one I use it for. I work, and work, mostly on the computer (It just *seems* like I live on the forums!) , but then I get frustrated at something, or burned out. Well, if I play something fairly mindless, yet which requires the mind to think about something else, I take a breather, and afterwards can usually go back at my task.
If I went and picked up a crossword puzzle or something, I'd be a lot longer. Put the computer aside etc. etc. I might even be tempted not to cont. with work right then.
3 ~ If you are alone, it's more social and interesting than a word search, and a lot less mindless than T.V. (I vaguely remember that about T.V.!)
Does that make it seem less useless to you, or no?