I'm working on an enterprise CMS which supports many user roles and generates highly configurable content.
A typical content entry form might have 8 text inputs, 6 checkboxes and a textarea.
A typical use-case will only involve perhaps 3 text inputs, a textarea and one checkbox.
A power-user may need any of these interfaces at any time and they need to be easy to get to.
My feeling is that having an "Advanced" slide-down with the less common features inside would make it easier for most users to use. I believe that people will be used to the convention of "If you can't see what you need, try the advanced section". I would also allow power users to set a value in their profile so "advanced" is open by default for them.
Would this make the site easier to use? Is there good evidence for this practice?