A Personal Dashboard is each user own dashboard. The user is free to add or remove widgets. Project Team members can not access each other personal dashboard.
Shared Dashboard is to share general graphs with others. Any user can create a Shared Dashboard and define team members who can access it. A shared dashboard can only be edited by its creator. Other team members cannot make any changes on the board.
Project Managers and Scrum Masters usually create a shared dashboard. Such board helps to make team aware of important factors of Project progress.
Note: Only an Admin can export data values of a widget by clicking on Ellipses icon and exporting detailed CSV.