I use i3 as well, I think it provides a lot of the advantages that tmux does but there are some features that tmux adds which can be useful. You mention persist

I use i3 as well, I think it provides a lot of the advantages that tmux does but there are some features that tmux adds which can be useful. You mention persistence, which is sometimes handy (though you will need a plug-in like tmux-resurrect if you want sessions to persist after a reboot). The main advantage I’ve found with tmux (along with something like tmuxinator, tmuxp, and now Smug) is that you can set up complex layouts containing multiple windows and panes. Then you can launch that layout with a single command. For instance, I’ve setup a system monitoring layout that launches htop, glances, tcpdump, and so on with the setup, sizing, and configuration I want. This capability is often useful for project specific arrangements and any kind of complex setup that you might want to reuse at some point in the future.