What functionality is missing? What is unsatisfying with the current situation?

On the Articles & Categories page there is no 'Expand All' button for the category browser, and when the page loads, the categories are collapsed by default. If making small edits to multiple pages within the same nested sub-category, this leads to multiple clicks just to get to where you can access the article. For example, if you have World>Science & Tech>Ships>Military, that represents four clicks before you can even select the article to edit...four additional clicks for every single page within that category that you have to edit. This can slow down the work flow dramatically.  

How does this feature request address the current situation?

  An "Expand All" button would expand the entire tree, allowing the deepest nested option to be selected on the second click. If the additional measure of 'remembering' the trees expansion state was taken, that could be reduced to a single click for subsequent page loads, dramatically reducing the number of clicks required.  

What are other uses for this feature request?

  This request is a work flow optimization measure for an existing feature, not a new feature in and of itself.