There’s Always Space On The Dashboard

Dashboard is automatically assigned a Space in Mission Control. If you like using Spaces (alternate Desktops) to control screen clutter, you might want Dashboard to relinquish its automatic assignment so that you can use that Space for something else.

You can uncheck the Show Dashboard as a Space option in the Mission Control preferences, but it won’t open up another Space. Even if you never use Dashboard, its Space is permanently reserved.