Once you leave design and layout to non-designers/non-layouters, they will ruin everything, and you will get angry calls from the companies' designers, complaining about how their beautiful design was ruined by someone using Comic Sans on a header. I've seen it happen. This is why CMS makers know that editors / article writers should not be allowed to design/layout pages.

Ideally, a WYSIWYG editor in a CMS should only allow users to use bold, italics, links, and perhaps insert small images. Anything more than that, and your web pages end up looking like MySpace/GeoCities.