Most word processors today are "What You See Is What You Get" (WYSIWYG). They're relatively easy to use, they let people easily change visual aspects of their writing to be a close approximation of what they want, and ... uh... Yeah, that's pretty much it.

The problem with WYSIWYG is that it is based around visual design. For scientific writing, particularly for larger documents, the emphasis is best placed on the logical design of the work. What is the logical purpose of each part of the document? Is it a section? Subsection header? Abstract? Title? In writing, we want to deal with what is written, and why, and then worry later (if at all) about how each part should be formatted.

Instead of WYSIWYG, LaTeX provides WYGIWYAF.