I like generating long LaTeX documents from org-mode because, for one thing, org-mode has nice section folding. But not everyone I work with uses Emacs, so its better to work in LaTeX directly rather than have Emacs generate LaTeX.
AUCTeX has section folding for LaTeX documents, though so far I’ve only has limited success at getting it to work. However, RefTeX worked right out of the box.
If you enter reftex-mode ctrl–c = then RefTeX will open a table of contents window.
Scrolling through the table of contents window scrolls through the body of the document. This isn’t exactly section folding, but it serves a similar purpose.
RefTeX ships with Emacs, so there’s probably no need to install it, but the mode is not enabled by default.
The built-in outline-minor-mode (https://www.gnu.org/software/emacs/manual/html_node/emacs/Outline-Minor-Mode.html) works well for folding LaTeX documents – I add it to LaTeX-mode-hook so I don’t forget to turn it on