That is probably one of my biggest pet peeves. It totally irritates me when I check a checkbox and something wacky happens (since any action or command (other than simple UI control hiding) that is fired off when you check a checkbox is wacky). A checkbox is supposed to represent a state: on/off, true/false, yes/no… or in the case of mixed state checkboxes: yes/no/kinda, true/false/true-for-some-but-not-all-but-you-don’t-know-which. You get the idea:

As the Windows Vista User Experience Guide for Check Boxes explains:

Don’t use the selection of a check box to:

• • Perform commands.
  • Display other windows, such as a dialog box to gather more input.
  • Dynamically display other controls related to the selected control (screen readers cannot detect such events).

What those three points basically sum up to is don’t do anything that isn’t obvious just by looking at the dialog. If you have disabled subordinate controls beneath an unchecked checkbox, it’s pretty obvious that checking that checkbox will enable the subordinate controls.

Now it wouldn’t be obvious if checking that checkbox also popped up a modal dialog, or sent an email to your boss telling him that you’re leaving work early.