Previously it was very easy to move a workbook from one project to another, but that wasn’t possible for a datasource. Instead one had to delete the original datasource and republish it seperately to a new project. However this broke any workbooks that used it (until they were updated and republished with the new location) so was not very fun.
However, now there’s a lovely new “move” button on the datasources page. This will save much frustration!
One use-case for this typically surrounds testing. Test datasources can be put into a suitable test folder, used for a while by those who want to. Then when confident that they work, they can be promoted to a more accessible and governed folder.