You can also set any number of standard layouts that you like, and toggle through them with Mod-Space. So full screen could be the primary one, two-pane split screen the secondary one, all windows visible be the 3rd one, etc.
And as others have mentioned, using this in conjunction with virtual desktops is quite powerful. E.g. moving windows between desktops is just a key combo and is very quick, so it's easy to switch between full screen and side-by-side of any two tiles just by moving one to the same desktop as the other.
My personal hot take is also that most people who think they really need another monitor are just addressing these symptoms because they're exhausted by alt-tabbing through 15 windows. They would be more productive on a single screen with a nice workspace configuration, though there are of course plenty of good reasons to want multiple monitors.