I don't think there is any reason to disable them honestly, unless you are trying for 6 ghz or something, and even then I can't say they'd matter. They don't seem to be hindering overclocks this time around and I'd leave them on for 24/7.
Here's a SUPER in depth article on them, if you are so inclined:
http://www.hardwaresecrets.com/article/611
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