@samurro Speed. For example, if I use Win+3 the focus moves to the window placed on the top monitor which is where workspace 3 is. I don't need to select the window from the list as I do when I use Alt+Tab, I just select the window because I know where it is.
I also don't need to drag and drop to get rid of windows I don't need at that moment. I open them and they go to the desired workspace and monitor automatically.
Here you'll find some clues https://odysee.com/@thelinuxcast:4/how-to-manage-multi-monitor-on-i3wm:5