I'm not a super sophisticated user of it.
I appreciate ability to arbitrarily split panes vertically or horizontally and also moving windows around with alt+shift+hjkl. Alt + enter brings up a new terminal.
Ctrl + d brings up dmenu or similar "global search/run text input".
It's easy to jump around virtual screens/tabs (alt + tab#).
Alt+f full screens a pane.
Basically you don't need the mouse much and it uses hjkl so vim users like it.
If you get those, it's probably pretty good coverage for i3 fans.