I would actually explicitly pick switching from an already-satisfactory i3 setup to a Regolith setup as maybe not worth it (unless you're literally just doing it for kicks, I guess?).

In my case: I've done i3 setups before and then haven't main'd Linux in a bit, then when back on it tried to see how well I could fare with minimum system setup, and Regolith gave me a good-ish i3 config out of the box (along with dark matching GTK3 theme and terminal themes etc.). I did end up tweaking the files though to change up some keybinds and indicate fan speed + thermals in the bar. So it ended up being mostly 1) just a config starter (incl. most bar widgets you'd want) that I can also maybe rebase on if they update upstream in a way that matters 2) a way to get very consistent system theming across i3 setup and GTK.

Regolith is just a software suite like gnome-desktop that attempts to make a coherent i3 system without having to find solutions for the parts of the desktop environment that i3 doesn't manage.

Advantage of using it is you get a set of sensible defaults rather than having to put together your own.

If you're an i3 veteran there is little if any advantage to switch. I was turned off by Regoliths' key bindings which deviate from vanilla i3.Regolith does have some nice features like parsing your config to display a helpful key map.