Spaces is what used to known in Linux as virtual desktops (maybe it still is), and that is how I think of it. Or as virtual monitors. Right now I have desktop one for local system iTerm2 and Firefox, desktop two for client 1 (terminals, IntelliJ IDEA), desktop three for client 2 (VirtualBox, terminals), desktop four for incidental stuff that needs a mostly empty desktop, and desktop five for Chrome (for things that need it), and GIMP and Inkscape (as needed). This way everything stays where I put it, including which windows over which other ones. So I can switch to D1 to look up some documentation on a function, then back to D2 to use that knowledge. Or on my personal laptop I can keep my coding project up one desktop and do the daily web surfing on another, and just switch desktops to have the coding project right where I left it.

(You do use a window manager, btw, it's the thing that puts the title bars on your windows and lets you move them around. On macOS it's integrated in, but on Linux you have to choose one. There are many, all of which have some failing. Except for sawfish, whose failing is that it is no longer maintained.)

Sort of. With proper workspaces you land directly on the full screen program with a single hotkey. No cmd-tab switching needed.