Scrolling.

That's a key feature when you don't reflexively use less and ] isn't a natural keybind for "let me scroll please".

Yes.

Window management, mouse support, key bindings (I really dislike the defaults for a few of them), selection/copy/paste, macros etc

All stuff that doesn’t need to be configured but if you look at any tmux tutorial you’ll see boat loads of details about. Which can be confusing because how do you know if you don’t need to know it?

Also what’s the basics for one person isn’t going to be the basics for another. Eg I rarely use the detach capabilities these days whereas the panes and windows are something I do use lots.

My point is this: tmux is sufficiently complicated that a complete beginner might not know what features they need to learn.

tmux does support scrolling and copy-paste, but they often work subtly differently than the way they do in a native terminal. For example, when I try putting `set -g mouse on` in `~/.tmux.conf`, scrolling mostly works fine but if I scroll up and then start typing or press up, I won't jump right to the bottom of the session the way I'm used to in native Alacritty (which I will often do as a way to return after scrolling back through a bunch of print output). This isn't a huge deal, and you can definitely get used to it, but it can be frustrating if you like how your normal terminal emulator works and don't want it to change.

That gets you scrolling, yes, but not in the same way as without tmux.

Without tmux, your terminal emulator uses its scroll-back buffer to render as you scroll, not requiring any intermediate copies of the lines of text scrolling into view.

With tmux, your terminal emulator no longer handles that, and instead tmux must pass a copy of each line freshly scrolled into view to the terminal emulator, which involves an intermediate copy of that text and re-triggers the terminal emulator’s parsing (as far as your terminal emulator is concerned, it has never seen this line of text yet). All of that (and some other subtle overhead I’m not mentioning here) are completely avoided outside of tmux (or more specifically: whenever the terminal emulator is free to manage its own scroll-back).

Well potentially some, but definitely not tiling and screen splitting.