While 'letting chaos reign' might seem the best solution, we've found that it also presents unforeseen accessibility and general readability issues, e.g, entire pages of bolded or inappropriately colored text, not to mention making entire websites look like, well, crap!  We also use a CMS (here at UC Irvine Libraries) and we do lock down certain styling functionality in the WYSIWYG, or define our own styles and limit editors to using those.  We also don't give most editors access to the HTML source code, which helps to prevent those ambitious self-taught HTML coders from straying too far from our defined style specs.  Most CMSes also offer workflow functionality and, in some cases, we do use that to assign a reviewer for certain departments who is the only person allowed to publish for that department, although many departmental staff may have permission to edit.
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Mark Vega
Programmer/Analyst
University of California, Irvine Libraries - Web Services