It adds tiling to floating window managers like openbox, xfwm, and kwin, giving tiling to more mainstream desktop environments like GNOME, XFCE, and KDE. It's not really made for i3 users I think.
I guess the advantage over i3 would be that those desktop environments have better integration with certain apps and a coherent look and feel. For example, on Ubuntu, which uses a modified GNOME, you can add tiling while still enjoying stuff like the volume control widget, gnome-control-center, consistent file open dialogs, and so on.
Stuff like Regolith is great, but do yourself a favor and invest some time in making your desktop your own - it makes a world of difference in terms of efficiency, and you get to learn how all these applications work, what they're capable of, etc.
I agree. I've only used regolith once, and it was a work computer that I didn't feel like copying my config to and didn't want to spend time configuring from scratch. It was nice in that case.