What's the difference between cloning and sharing custom dashboards?

A shared dashboard will be the exact dashboard that you created shown as a read-only version to all other members of your organization. Cloned dashboards will essentially save a copy of your dashboard to specific individuals' accounts. Once they have a cloned copy, they will be able to modify the data and widgets.
To share a dashboard, click the "share" button at the top right of the dashboards page or share in the dashboard manager. You can also share multiple dashboards at the same time in the dashboard manager by checking the box beside one or more custom dashboards and clicking the "Share" button that appears at the bottom of the modal. No one who is able to see the dashboard will be able to modify it other than the original person who shared it, except to view different lookback periods.

To clone a dashboard, enter the dashboard manager and check the box next to one or more custom dashboards. A "Clone" button will appear at the bottom, which, when selected, will allow you to select one or more individuals in your organization to share the dashboard with.