I'm guessing you don't see this when it's castled king-side. The king is not as exposed after it moves over.
Why Does the King Move OVer?
There's no dark squared bishop to pin white's Q. Exposed to what? And yes, i often see it on the other side too.
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Excuse my ignorance, but i've seen this move many times and don't know why the king, after castled, moves over, seemingly giving up a tempo. Here's an example: 1. e4 e5 2. Nf3 Nc6 3. d4exd4 4. Nxd4 Bc5 5. Nb3Bb4+ 6. Bd2 a5 7. a3Bxd2+ 8. Qxd2 Nf69. Nc3 O-O 10. O-O-O d611. Kb1
Thanks for the help.