You and I have almost exactly the same setup. I also usually only have a browser and terminal/tmux running.

If I'm reading the general web then I max the browser (which also maxes the terminal, since I'm running awesome-wm tiling window manager).

If I'm writing code or anything else terminal-focused, then they're unmaxed, side by side.

If you are already going that far, why not just switch to a tiling window manager?

They are not mutually exclusive. I use xmonad, tmux, and vim together. Tmux adds some niceties on top of xmonad like shared keybinds with vim making moving across vim panes and terminals seamless. Also, I can jump on my macbook and login to my desktop using mosh and re-attach to the tmux session and continue working where I left off.

I do, but...

If I'm on my laptop, then switch to my desktop, a twm doesn't save my sessions. Tmux on a remote machine does.

Me too, and it's great and even works on Windows with Babun :-) If I use tmux as window manager, I don't have the problem with installing fluxbox etc. on Windows :-)

Same setup with a bunch of pdf open as well. Any idea how I could stop having so many papers open? (I'm on macOS)

I don't know macOS very well, so probably not, but what do you mean by "so many papers open" ?

just a lot of different PDFs open.