I'm a long time i3, tmux, vim/nvim user. You can see a pattern. When I write code, I typically have a bunch of i3 and/or tmux windows open with dedicated tools ready to execute the necessary commands. Linters, compilers, containers, http clients, db clients, REPLs, log viewers, doc viewers, notes, tests, etc. All nicely organized and readily accessible a few finger taps away.
For the longest time I've only used a dumb variant of autocomplete that is scoped to only suggest names found in files that were loaded in the current editor session. It's not context aware like an LSP would be. It may sound bizarre, but I never really felt that I missed much. C-P/C-N, scroll one or two items away and most times I get what I want. If I needed to use an unfamiliar feature, I'd open my past notes or the docs and skim through them, or I'd reach for the REPL. But working like this, I think you also develop some extra awareness and other tacit optimizations that reduce the need to do this sort of things often. You remember many small details, you develop a knack for taking notes, you get efficient at using external tools, you learn to quickly access docs from REPLs, that sort of things. Someone else mentioned code organization in a comment. That's definitely a big deal.
I've often been fascinated by the approach of transforming the editor to integrate all the things for which I have separate tools. So I decided to try it out for a few months (Neovim has some powerful plugins). I ended up keeping some of the suggestions, mostly the ones that aid in navigating the file system within the editor and finding files (e.g. Telescope). But I think my LSP experience has been one of the most distracting programming experience I've ever had. Perhaps if I'd given it more time, I might have gotten use to it. But it felt less productive for really marginal gains.
I think describing my experience can bring to light that some of us prefer working depth-first, while others are comfortable breadth-first.
The "real-time" nature of the warnings and suggestions was inappropriate for me. It felt like trying to write an essay and being told to worry about form and grammar, while I'm still developing my thoughts. Laying down the foundations of what I'm trying to express and meanwhile things popping up in my face completely out of context. By context here I mean at the wrong time. I'm currently laying down the structure of my thoughts and I see the editor issuing warnings about syntax or wrong imports. Please, this is not the time. Let me think. Stop distracting me. I'm ok to not have it right on the first try. When I run the damn thing, you can complain all you want. Don't worry, I'll understand what you want and will fix it. Right now I need to think. This is not grammar time.
The fix for the above was to configure the LSP to be mostly silent and on-demand. But then there wasn't much difference to using it externally to the editor.