It’s very easy to sit down at a keyboard with a traditional wordprocessor and just start typing. If it’s a very short document, or something transient or relatively unimportant, then you just want to type it in and make it ‘look right’ by highlighting with the mouse and clicking on font styles and sizes.
In doing so, you may achieve the effect you wanted, but your actions have left no trace behind of why you made these changes. This is not important for trivial, ephemeral, or short-term documents, but if you write longer, permanent, or more complex documents, or if you often write documents to a regular pattern like reports or articles, then making them consistent by manual methods becomes a nightmare, and an enormous waste of time. LATEX’s facilities for automation are based on you providing this ‘why’ type of information.
If your documents have any of the features below, then you have probably already started thinking about structure.
The document naturally divides into sections (parts, chapters, etc).
The document is long.
There is lots of repetitive formatting in the document.
The document is complex (intellectually or visually).
There are lots of figures or tables (or examples, exercises, panels, sidebars, etc).
Accuracy is important in formatting the document.
A master copy is needed for future reference or reprinting.
This is a formal or official document needing special care and attention.
It’s my thesis, book, leaflet, pamphlet, paper, article, etc That’s why I care.
The document (or part of it) may need ongoing or occasional re-editing and republishing.
If you’ve got that far, you’re over half-way done. Using a structural editor — even a simple outliner — can make a huge difference to the quality of your thinking because you are consciously organising your thoughts before setting them down. And it can make just as big a difference to your formatting as well: more consistent, better presented, easier for the reader to navigate through, and more likely to be read and understood — which is presumably why you are writing the document in the first place.