Moving windows worked within workspaces (click, drag, drop) same as across workspaces (click, drag, drop).
Basically the principal of least surprise. Moving the mouse and clicking shouldn't have special rules across workspaces unrelated to the rules of working within a workspace.
So basically you could basically intuitively work on a space much larger than your screen without having to think about it.
Ubuntu 18.04 forces vertical workspaces (so 1x4). In the dual monitor config it only moves the left monitor across desktops. And moving windows between workspaces is a nightmare. Step one is move the mouse to the top left corner and click activities to expose. Step 2 displays all your windows as tiny icons, 2/3rd of your screen is just the background, so they aren't much bigger then icons, and theor position once exposed is unrelated to the original position. So now you have to refind your window, then drop it into one of the workspaces. But you can't watch or tell where it lands. So then you have to switch workspaces and refind that window.
Quite the pain compared to 16.04 (or any decent window manager since olvwm 20+ years ago) it's just drag and drop.
Additionally there's no spatial relationship. So a window that's off your top edge of your workspace doesn't show up in the workspace above yours. It's basically just 4 unrelated workspaces. They also prevent wrap around, so you can't go from 1 to 4, but have to visit 2 and 3 first.
Reminds me of the first hacks to OSX and Windows to get more than one desktop. Linux folks figured this out 20+ years ago with olvwm, ctwm, and many others.