Once upon a time, there was a big scary web application named Launchpad. Its interface intimidated many users, so the authors gave it a `Help' button in the top left-hand corner. A user could click on this at any time to bring up a help dialog. Unfortunately, the Launchpad didn't feel the need to actually fill the help pane with any content, yet continued to show the button nonetheless. Thus, users got infuriated, and learnt that using the button was useless. When actual help content was eventually added, it was missed, as no user ever expected the button to yield anything useful.
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Seriously now, hiding the Help button when there is no useful content is likely a better idea, as everybody has now learnt it's a waste of their time to click it.
Good call.