It's quite configurable, allowing different key combinations for different window arrangement functions, but the most useful one is that it allows you to bring a single window from another application to the top without rearranging the rest of the stack. This is useful if you are switching back and forth between windows from two different apps each of which has several other windows open, for example a browser and a text editor.

There is no way to map Cmd+Tab to Alt+Tab in MacOS. Which makes for an extremely frustrating experience in muscle memory when alternating between your work Mac and your personal Linux/Windows machines. This was the biggest grievance to me.

But the Cmd+Tab behavior is also incapable of switching between multiple open windows of the same program. So if you have two Firefox Windows open, you can't switch between them with Cmd+Tab.

Cmd+Tab also has the annoying behavior of listing programs that are "running" but do not have any open windows. I still can't for the life of me figure out how this would be useful to someone.

Oh god that last one drives me up the wall. It entirely defeats the purpose of using a keyboard shortcut to switch applications if you have to move the mouse to open a window anyway. It's beyond me why MacOS wouldn't automatically restore the most recently minimised window, the way literally every other DE does.