Even the chance is that, that most users are aware of the LaTeX software already it makes sense to emphasize the advantages again and again. The first thing to mention is, that most desktop publishing software from the past is gone. Software programs like Ventura publisher, Word for MS-DOS, Framemaker and even quarkxpress are forgotten. They were replaced by other tools. Only the LaTex has prooven it's stability over decades.
The perhaps most common question is, why should somebody learn LaTeX if he can typeset the document with MS-Word much easier. The greatest advantage is, that similar to the txt2ps command line tool under Linux, the LaTex program can handle easily larger file. It is not difficult to create a pdf file which has 3000 pages, contains lots of graphics and archives all the issues of journal. This feature is missing for possible alternatives over TeX.
Instead of describing how LaTeX was used 20 years ago it makes to give a short outlook how a modern approach is to creating print ready document. First step is to create a document in an outliner software like Emacs, Lyx or Emacs. This step needs time and has nothing to do with desktop publishing or typesetting. If the text is ready the funny part starts. The text is converted into the LaTeX format and converted in the pdf format. With the help of a template this step needs only a little amount of time. Even the amount of LaTex documentations is high and the possible options are endless, the average user will spend only a little amount of time with the typesetting software. It is basically a rendering engine which takes a raw text and produces a pdf file. This pdf file can be printed, uploaded into the internet or copied on a cd-rom.
Somebody may argue, that the ability to create a pdf file with 3000 pages is not a big thing and other programs like indesign or Word can do the same. No they can't. In contrast to a common myth, text processing is a computational demanding task. A single jpeg image with 300 dpi can have lot of megabyte in size. It makes sense to avoid WYSIWYG software and take advantage of desktop publishing software for handle the document creation process.
___Whats after LaTeX?___
The main advantage of LaTeX over alternative desktop publishing software like Word and Indesign is, that the author can focus on the content and ignores the layout. The problem of aranging the content in columns and place the images at the correct place is postponed to a later step and is handled by the latex software during a batch processing run. This reduces the obligation of the author to creating the text.
The interesting situation is, that LaTeX is not the advanced software for focusing on the text. What authors are using in the reality instead of LaTeX are outlining software tools. These gui applications have usually on the left side a pane in which the sections of the text can be arranged. Famous helping tools for the LaTeX software like Texniccenter and Lyx are providing an outline capabilities but many other tools outside of the LaTex ecosystem are available too.
From a technical perspective these programs are emphasizing the difference between text and layout much further. An outline only tool like cherrytree doesn't provide any ormatting capabilities but it is focussed on the text itself. That means, the dimension of the age are missing and most images are shown in a draft mode. In most cases outline tools are used for making notes. But they can be utilized for writing longer texts as well.
It is important to known that an outline tool is different from desktop publishing. Some outline tools are supporting the export of the file into the pdf format, but the quality is low. Instead, outline tools are trying to structure the text on a semantic level with the help of sections.
The simple reason why so many authors are fascinated by the LaTeX software is because it handle the layout process automatically. After the some decision were made about the amount of columns, the font and the size of a section, the latex software will layout the text by it's own. It fulfills the promise of database publishing.
The perhaps most impressive example for the strength of latex is the lyx software. Lyx is some sort of outliner with a pdf export option. Lyx asks the author to provide the text which consists of a hierarchical paragraph and then lyx can export this document into the pdf format. In contrast to alternative outliner software like cherrytree, the pdf file was typeset with the latex backend which is equal to get a high quality result back.
Let us construct an example. Suppose the user provides the lyx file for a 2000 page long book. The file contains of the raw text, which are the paragraphs, the sections, bibliographic references and tables. What lyx can do very well is to confert this raw text into a fancy pdf booki.
Sometimes the Lyx software is described as a dtp software similar to idesign or Word. But it's not. Lyx has more in common with outliner software like cherrytree, texniccenter or Omnioutliner on the mac. It's purpose is, that the author can enter notes and paragraphs.
___Outline editor___
Let us take a closer look at the cherrytree software. There is a similarity between cherrytree and Lyx. Both programs have on the left side an outline pane and the user is able to enter text, items and tables in the main window. The advantage of Lyx is, that it can generate a well looking pdf document on demand, while the export option of cherry tree is reduced to create a html file.
The similarity between lyx and cherrytree is that in both programs a document contains of a hierarchical structure which contains of sections, subsections and fulltext. It is possible to jump between the section with hyperlinks and a table of contents is available as default.
Suppose somebody invents a cherrytree plugin which allows the run the external latex engine with a command line. Then the cherrytree software will behave the same like lyx. The interesting situation is that cherrytree is widely recognized as an outliner tool. This is the correct description for these software programs.