The real power of tmux, though, is that it manages the session you created.
So, one use case would be saving your current terminal setup. Instead of exiting the terminal and navigating to the project and setting up the environment again next time, you can simply detach and re-attach.
systemd: Oh yeah? Hold my beer
I settled on two.
Arch for my desktop, because there I like having an always up-to-date system with the latest drivers and libraries so that I can always try the latest versions of whatever it is I want to play with next. Pacman is also a pretty good package manager, and almost any piece of software that is not in the default repos can be found in the AUR. For the rest, I also like that Arch just gets out of your way and lets you configure your system how you want.
Debian for anything that runs unattended, like all my homelab services. It’s well tested, offers feature stability, has long-enough support, and doesn’t do weird things every other release like forcing snaps or netplan or cloud-init on you. Those “boring” qualities make it the perfect base to run something for a long time that doesn’t scream for attention all the time.