Can't tell when data source connects to 0 cards and 0 flows/ETLs
The datasets tab in the data center tells you how many cards are connected to a data source.
The dataflows tab in the data center tells you what data sources contribute to a flow (though you have to hover your mouse over the input/output column to find this out).
There is currently no way to see that a dataset has both 0 cards AND 0 connections to dataflows and therefore can be deleted.
Hoping this is ocming in the new datacenter enhancements, but wanted to add to the Dojo in case that hasn't been considered.