when i first started using linux i didn't touch them. now i can't imagine not having them.
i'd have everything open for work and my wife might sit down and use the pc, sometimes disrupting my perfect order or close a browser window by reflex.
so i got her to use a separate workspace when she used the pc.
then i started re-organizing my workflow, leaving my email open in one workspace, programming in another, etc.
you can always move your window into another workspace if you find you are switching too much.
it's very, very convenient when you get used to it.
ctrl+alt+arrow keys for quick switching, add a shift to that and you throw your window into the next workspace. map keys to specific workspaces.
imo it's one of the best things about linux desktops.
compiz has a great plugin called 'expo' for dragging windows across workspaces in zoomed out view.
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Alt-Tab and Expose take too much work if you use multiple apps in a "thinking cluster" notion.
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i never got the alt-tab thing. more than 2 or 3 windows open and its slower than clicking.