Emacs is ancient bit of software that is the fanciest text editor around. It's like a shark in that it hasn't evolved in years but is perfectly suited to what it does. I use it a lot, mainly for org-mode, which is an outlining system that allows you to fold parts of your document, hiding them from view. You can also assign statuses and dates to different headlines, meaning it works as a task manager as well. I use it for writing and also to organise my life.
I have one file for all my poetry over the last five years that is only 200kb in size and in plain text . I can quickly search through the document to find the poems I want. I also have custom statuses set up, so I can see which poems I have sent to publishers and which ones need revising. If I'm arranging poems into an order for a book, I can quickly move the headlines and content around. Plus, almost everything is assigned to a keyboard shortcut by default so it is fast to navigate.
That said, I wouldn't necessarily recommend it to anyone unless you are prepared for a fairly steep learning curve. Because it's a thirty year old piece of software, it has interesting quirks that are difficult to learn. You may find you are spending more time messing with the system when the tools don't matter as much as the words. I took a long time messing around with irrelevant setups before I focused on what matters.