If you mean vs. not using screen or tmux, the pros to using (among many) are:
1) you get plural terminals in one "window" (xterm, remote ssh session, etc.) that you can switch between with hot-keys. This has a larger advantage for remote ssh sessions, where one ssh connection can be used for plural remote terminals, than it does locally where you could simply launch a second xterm.
2) you gain the ability to 'disconnect' from the screen session (I presume tmux offers a similar feature). This works just like 'disconnect' from a RDP session. All your remote terminals remain active, open, and waiting. When you next ssh in, you simply 'reconnect' and everything is there just as you left it when you disconnected. This helps for both flaky connections where the link drops at times as well as the "done for the day" "disconnect".
3) for screen, there is a screen built in 'copy and paste' controlled by the screen hotkeys, so if you are in a situation where you have no local copy/paste (unlikely in 2024, much more likely back in the days of VT100's) you can still select and copy portions of the screen to a 'clipboard' for pasting into somewhere else. I don't know if tmux offers something similar.
4) screen also offers 'scrollback buffering' (it will retain the last X lines that scroll off the top of your viewport) and has a feature to let you "look back" at what just scrolled out of view. This is less useful in 2024 with xterms/urxvt's offering the same feature locally, but for a remote ssh connect this does give you 'scrollback' that is specific to each screen terminal you have open instead of all mixed up in the local viewer.
There's more advantages, but those are the big ones, and the 'disconnect/reconnect' one is huge if you use the terminal a lot and also often connect via ssh from remote locations.
Killer feature: mouse scrolling works out of the box.
The only problem is that projects dealing with network stuff require aging just the way wines do. Networks are unreliable and can get into a thousand different states that are a combination of local connection issues, remote issues, input problems, etc etc. I found (when I tried it a year or two ago) that Zellij could handle a decent amount of such weird states, but not all of them. There was noticeably more "stuck" states it could get into.
It was a pleasure to use in every other way, and maybe this has become much less of a problem in the intervening time. I'm pretty sure that Zellij is going to be my one true term mux for the future, just not sure that future has started yet.
screen /dev/ttyUSB0 9600An example from man tmux -
"
refresh-client -t/dev/ttyp2
rename-session -tfirst newname
set-option -wt:0 monitor-activity on
new-window ; split-window -d
bind-key R source-file ~/.tmux.conf \; \ display-message "source-file done"
"
Screen has no equivalent besides manually using the keybinds.
I believe tmux has some better mechanics around the attach/detach but it eludes me atm what was better.
Basically what made me switch in the first place from screen to tmux was wanting a split window watch compile and a logfile to run automatically with one command.
Hard with screen and easy with tmux.
* Are there particular pros and cons to using screen or tmux?
(I'm generally on macOS for work, but never really go into using iTerm2, so that integration isn't a big thing for me personally.)
Edit: I mean why use one over the other. I generally use something on the destination host I'm SSHing to in case the network goes sideways.