It's a bit arcane written that way, but each workspace is a tag. Pressing Mod4 + Control + 2 means to show workspace 2. The effect is cumulative. If you now press Mod4 + Control + 3, it will be showing both workspace 2 and 3 simultaneously (and tiling the combined set of windows).
If you press Mod4 + Control + 3 again, it will remove workspace 3 from view.
If you now just leave to go to some workspace, (e.g. Mod4 + 5), it will only show workspace 5.
If you press Mod4 + Control + 3 again, it will remove workspace 3 from view.
If you now just leave to go to some workspace, (e.g. Mod4 + 5), it will only show workspace 5.
Can't live without it.