Edit mode is one of the two states of the dashboard. In the Edit mode you can add and/or remove widgets, and generally do whatever you want with your dashboard. Reporting mode is the state of the dashboard as your client sees it.
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You can toggle between the two on the left sidebar.

Besides adding and removing widgets, in Edit mode you can also customize your dashboard (General & Style), add a password to protect your dashboard (Security), add widget sources or archive your dashboard.
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